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.