can you explain what distinguishes this from other configs

This config is magic instead of those stupid console commands

seems to try and do multiple things (graphics cfg and stuff like null-movement) all mixed together and not clearly separated. I'd recommend separating them out and trying to be more focused with it, like:
https://github.com/mastercoms/mastercomfig - very well focused on doing everything graphics
https://github.com/JarateKing/jarconfig - focused on many gameplay scripts

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As for some specific stuff:
do I use "autoexec_performance" or "pretty_gfx"? There's a lot of overlap between them, but there's also a lot of stuff that is in one but not the other, and it's not really clear what's what.

// Net graph script for TAB
alias "+netgraphscores" "net_graph 4; +showscores" // can change to 1 for fps improvement
alias "-netgraphscores" "net_graph 0; -showscores"
bind "TAB" "+netgraphscores"

I'd recommend going with something more like: https://gamebanana.com/scripts/9167 - the scoreboard script you have is a pretty common one but it can be done better
I wouldn't have a bind like that in the middle of the script where it's hard to find, as well. If I didn't have scoreboard on tab, I'd be very confused why tab randomly became scoreboard using this script.

incrementvar mat_managedtextures 0 0 1

incrementvar will increase the setting between a min and a max bound. The bounds here are 0 and 0, so this should always set this to 0. May as well just be "mat_managedtextures 0".

fps_max 300 // can't tell difference between this and 0

fps_max 0 disables the frame limit. 300 puts a cap at 300 fps, which is obviously not going to be different if you don't get that much fps but some people do and a 300 cap is very different from uncapped.
There's a decent bit of valid debate around whether this should be 0 or 995 or whatever you can reliably get stable (and some wrong arguments about 2x your framerate or whatever) but in general this isn't the sort of thing that's just found in the middle of your cfg (in autoexec_performance, it is at the bottom of pretty_gfx).

I haven't given it a thorough lookthrough (I didn't read through all the actual graphics settings and I'm not the best to comment on them) but in general this cfg doesnt appear to have any clear direction it wants to go in. Seems more like a hodgepodge of random settings from other things rather than actually trying to improve on what's already out there. I don't mean to put it down but cfg's are among the hardest thing to make good in tf2 and require a lot of effort to be decent, and I'd recommend trying to deeply understand what other people have done and how they can be done better before working on your own.

Thanks. I’ll mess around with it some more and see if the amount of extra garbage can go away

don't download this!!! I installed it and it made my game look all low graphics like Minecraft

I thought I enabled the settings so it wouldn’t have those pixelated textures. Could’ve been wrong