Google runs the Debian derived distro “gLinux” on their own internal workstations.
HP runs their internal infrastructure services on Debian
Most global ntp servers run Debian
The vast majority of the cloud runs on Debian or debian derived distros.
CERN recently migrated from RHEL to Debian Trixie -
As per their slogan, Debian is truly “the universal operating system” 
I’m pretty confident Debian and its derivatives would make up the majority of Linux distribution uses out there.
These days, the phrase " and its derivatives" is what truly makes Debian shine.
With Debian, it’s a fantastic server environment.. Many of the Debian derivatives bring out other characteristics. The one I use, antiX Linux, is outstanding across of wide range of aging systems, with the consequences that you have to create your own variations or “respins” if you need the latest kernel to support very recent hardware, or you change the mix of applications because the ones provided are intended for systems from 5, 10, 15, or even more years ago.
Another alternative is MX Linux; a middle of the road distribution fine crafted as an easy to use, modest resource, general purpose system. Often it shows up on the “Leader Board” of distributions simply because it’s reasonably easy and works well.
Then there’s the alternatives that come from business ventures, such as the *buntu variations produced by Canonical or the plug it in and go versions from the Linux Mint project.
Enthusiasts go in different directions; sometimes those “ready to go” distributions do not appeal to the do it yourself hobbyist, but the value is that they work well; that’s all that some people are looking for.
Besides efficiency, I’ll tell you what I like about both the MX Linux and antiX Linux projects: both have a really good collection of tools that allow people an easy way to back up their systems that also happens to be a great way to tailor, customize, and repackage your own setup, all while creating a useful backup image.
These are things that can be done with Debian alternatives, but the firm foundation has been put in place by Debian developers, enabling repackagers like antiX to do the things they want - such as scrapping systemd in favor of leaner streamlined process initiation and service management tools.
Not too long ago I pulled out my aging Dell Inspiron 5558 laptop and updated siduction, a Debian Sid alternative that emphasizes cutting edge software and high performance efficiency. Unlike antiX, siduction sticks with systemd and other standard Debian features, adding it’s own highlights by building recent vintage performance tuned system kernels and system utilities.
I hope I’ve given you enough examples of why a conservative Debian system with an ultra reliable core is only one of the many reasons why Debian continues to excel. The other reasons are that derivatives based on this solid foundation are able to create a multitude of variations, each that adds a distinctive set of characteristics. As much as their core foundation is similar, the surrounding components have as much variety and variation as the countries and nations of this earth.
Like the creatures of earth, at times there are contentious discussions and even strong disagreements; these often turn into forks in the road, and as long as there are no destructive wars, what emerges is a rich ecosystem with varieties as endless as the imagination of the individuals involved in their creation!
I’ve been using Debian derivatives since 2008, when I discovered Ubuntu, which worked perfectly on my laptop.
I’ve always been open to something better, and that led me to CachyOS, which is the most up to date and most optimized distro I’d ever seen.
However, the lack of a number of packages I’d used for years - e.g. dbench, diatheke, dsh to name a few, brought me back to MX Linux, because the performance was good enough, and in other respects it was superior to CachyOS.
Both thoughts are worthwhile. I’ve done some work with Cachy OS. What I can say about it, based on my experience with it, is that it offers various choices. One choice provides cutting edge system kernels, offering fast, optimized performance when you have the equipment to handle it; the other offers a slightly more conservative configuration to provide a stable environment.
After a few really good months using Cachy OS, I managed to break it twice within a short period of time, so I determined for my own use to stick predominantly with Debian based systems as you have BUT I do have ONE Arch based configuration that has been wonderfully solid and I’ve had it in place for between two and three years with no problems whatsoever; it’s called Endeavour OS and it manages to provide just the right combination of performance, features and stability.
A real hard core Arch Linux user builds their own Arch configurations; the rest of the world is well off considering Endeavour OS - it’s like taking a SAFE ride into space - and a few of their wallpaper designs even feature the Galaxy and other extra terrestrial artistry.
On the Debian end of the world, I’ve stretched the boundaries. Over the years I’ve had plain ordinary Debian systems at times, at other times I’ve held to the testing repositories and I’ve also had long runs with Debian Sid, both in Sid form and in variations from siduction, Kanotix and a few others. Most of the time on an average day, I use a distribution built specifically for aging systems called antiX Linux; it sheds systemd and uses runit, dinit, or other init alternatives and service managers to run very lean configurations; I can tailor it as I please and that has become my long time favorite distribution.
It certainly does. I won’t use anything else on my systems. Heh.
Viva Debian derivatives, meaning “Long Live the Debian derivatives!” (For me, that’s typically antiX for lean stuff, MX Linux for a super easy to maintain middle of the road desktop distribution. I don’t use straight Debian very much any more, but I did snag it immediately when Debian Trixie was released and I’ll do so again once Forky is released, plus I occasionally test siduction, a “Sid” derivative).
Yeah I’m sold on MX as a daily driver, but if there was no MX I could live with straight Debian
Me too! Actually I have some of both now; the Debian is currently on a USB but siduction is installed on one of my older systems; easy to get builds going for either style; I have years of actual experience with all of them.
MX is one of those distros I boot live to every once in a while because it’s a solid distro. I look forward to their releases. There are some pretty nice Debian derivatives I play with every once in a while, and certainly might learn a new thing from.
Debian is real hot cocoa to me, though. A good stew. I mean, it’s mine, you know. I can trust Debian enough that I don’t have to mess with the system much, though there is a high probability for at least something - or I can mess with the system, a lot, and still rely on it and it never throws a fit or gets in my way - it will hold the door open for me as I cross the threshold to fall right over a cliff.
That’s the kind of relationship I want to have with an operating system: you had better reliably allow me to end myself and be quiet about it. I never found anything else compelling enough to bother changing to, to abandon my kung-fu for. By now it’s personal, I mean, I’ve “known” Debian longer then my children.
That’s not quite true for me because I used several other things before it; I used Unix systems from 1982 until I left Digital Equipment in 1998, but I ended up using either UNIX or Linux several more times in my various jobs.
As far as Debian goes, I had been using Linux for 6-7 years before I was able to really dig into Debian, but once I did, Debian or Debian-based systems have dominated 75% or more of what I use. Today I rarely build a straight Debian system; I use software BASED on Debian - as I mentioned one of my desktop units runs MX Linux; my typical daily system, including right now, is antiX Linux, a Debian based system that refuses to use systemd, so it has deviated from the init system that Debian now uses. At the moment my process init is runit instead of systemd or sysVinit. Instead of systemd, I use runit, sysVinit, S6-RC, S6-66, or dinit, but runit - the one I’m using now, is typically my default.
I use this distribution because it’s lean and simple; it was here that I tried out DORiS.