I wouldn't call advanced movement "speeding up Quake". Speed in Quake and other FPS is an important factor that influences what you based on the speed that you have. Bunny hopping, air control, rocket jumps are not as useful when the base speed goes up. Also, less maneuverability, like in Quake 2, and bigger maps, mean that you have to be more judicious about your next move, and plan ahead more, stock up on more items, etc. There is an important balance to these things.

I don't understand what PVS is in this context, but it seems any attempt to completely automate this would struggle with false positives.

There might be >350 polys visible from weird camera locations, but if the player is never there in normal gameplay you don't care about them. If they do end up in such a weird position in one game in a thousand (say a rocket jump lifts them up to somewhere normally inaccessible) it's not the end of the world anyway, the game will just render slower for a few frames.

The player speed in Doom is completely unrealistic, which is fun, but plays against immersion.

In Quake, the player speed is less insane, more in line with human abilities, and it makes Quake feel more real. BTW the same is true for System Shock, where the player is not a sprinter champion at all (but can obtain a skateboard, but this is another kettle of fish).

Every single YouTube video does this right now. They are all incredibly slow and take forever to get to the point (if there even is one).

I have heard this is because there's a magic duration number for monetization.

I often go to YouTube to find teardowns and repair instructions. One thing I have run across is this niche where some guy out gal repairs something very slowly, over the course of an hour or two, with the mic gain cranked way up even though they say absolutely nothing the whole time. When I look at the channel, all the videos are the exactly the same and they have very high subscriber counts. I genuinely can't imagine who is watching these and why. But they must make a ton of money on the ad revenue.

Since kiddos play them at 1.5, you would actually get a normal video :-P

Imagine walking around your 3d map hundreds of times on a slow ass computer looking for frame views that exceed 350 polygons. Must have been a pain in the ass.