It has been a while since I’ve used a Bullseye-based system, but my Bookworm systems had a very good run, in fact one is still going, but I’ve since put some Trixie-based systems together.
I think it all depends on what we do with our systems and how we use them. I noticed when Trixie came out that a few things “disappeared” but in every case I can think of, when one thing went away something else became available. Also, when I first started with Trixie it seemed like everything I did was costing me 20-50 MB extra in initial system footprint.
Just as I fine tuned Bookworm systems for many years, I’m getting to the point where my Trixie-based systems are getting in tune, so I would argue that efficiency hasn’t disappeared completely. I happen to use antiX Linux, which goes to great depths to keep as much efficiency as possible, and I’ve been able to fine tune it, even with antiX 26, their Trixie-based release, so it IS possible to keep aging devices doing some useful things.