Servers cost money, the client is free (and pays you sometimes)!

While I agree about devs should be testing on slow devices, the particular target audience of the site generally have pretty decent machines (including two that I have) and there isn't much reason for the site lag. It's not really doing any 3D rendering with complex shaders or video filtering; it just shows changed lines in two files. That shouldn't lag.

It is garbage even on my extremely high end desktop PC.

> the problem is developers having fast modern machines.

> if they were forced to use slow machines, they would not be able to put out crap like that

Lots of developers are rather obsessed with writing good, performant code. The problem is rather that many project managers do not let them do these insane optimizations because they take time.

The only things that forcing developers to use slow machines will bring is developers quitting (and quite a lot of them would actually love to see the person responsible for this decision dead (I'm not joking) because he made the developers' job a hell on earth).

What you should rather do if you want performant software is to fire all the project managers who don't give the developers the necessary time (or don't encourage the developers) to write highly optimized code (i.e. those idiot project managers who argue with "pragmatism" concerning this point).

M4 macbook pro and almost unusably slow

I don't think so, I think the problem is their devs work on tiny play pretend codebases or micro service architecture.

GitHub is big software, but not that big. Huge monorepos and big big diffs grind GitHub to a pulp.

Only in the ideal world, where developers test results of their work on their machines. Test for real, with real db, not with empty or mocks.