It's pure logic and simple physics, not an assumption. DOS is faster than NT, same way tinycore is faster than most linux distros.
You can't expect 'allyesconfig" kernel to build faster than 'localmodconfig' kernel and you can't expect to backup a full 1Tb drive faster than 5Gb drive.
It's just physically not possible, arguing otherwise is a waste of time.

That's not a very good analogy, IMHO.

DOS is faster than NT because it takes far less resources to handle a Single User- Single Application System even with a shell on top than a multi-user, multi-tasking full GUI environment.

Tinycore? What is there preventing turning off of services so that the resources footprint is similar on any Linux distro providing very similar speed?

I am not altogether certain that build time is affected by whether or not one answers "yes" or "no" but I am quite certain that options set to "m" where appropriate modules are only loaded on-demand will RUN almost as fast as one that behaves like an embedded system where only the hardware that actually exists is supported. That's why they are called "modules". The entire kernel does not have to swing to load and unload modules, afaik. Even if I am mistaken on either of those I will bet that at best a frame per second or so difference would be the result of any "shootout".

Backups of a smaller system, at least full as opposed to incremental, are obviously going to be faster than on a larger system. Since full backups are rare, that's not something I worry about.

So in terms of gaming performance, it is indeed an assumption that smaller will be functionally faster in game.

Normally it's the dependencies of dependencies, but not on Slackware which is one of the reasons I use it. There's only build dependency in it.

Regardless, there's weekly or bi-weekly updates to LTS kernels, and having a localmodconfig has saved a lot of time in the long run.
Building it takes just a few minutes, while if I had to build all modules it would take more than half hour to compile.

Full backups take long time to make, and the most logical procedure is to strip down what is mounted (i.e. root) so that you can do sector-by-sector backup in few minutes.

On the same hardware, it will be the same performance unless the filesystem is heavily fragmented.
Though I'm not very familiar with modern gaming, there was a time when I played games all day (mostly DOS games) but it was not a very popular thing back then, it was actually frowned upon.
Nowadays it seems just like any other hobby, they even made it a sport. Personally I'd rather do something constructive, as I already left like thousand euros at blizzard and gained nothing.

Topic is derailed, anyway I hope it works out well for the OP and he succeeds in building his system.

Report from the front line: I was naive thinking it would be simple. I was able to play on Knoppix 7.0 (Linux Magazine edition) but neither 7.2 nor 7.4. I tried Salix 14.1 Mate, it was catastrophic, without Nvidia driver I was completely unable to even start game, now as I installed Nvidia driver I can start game but there is no keyboard, luckily in Diablo 2 almost all things can be done with mouse.

There is Salix 14.2...been out for quite some time now...https://salixos.org/download.html

It was not my intention to blame Salix, I was rather tried to emphasize that Linux got similar problems like WS: no backward compatibility, some old games are as well unplayable on W10. This is how things are going: new not necessary is better but is new and shiny.