This is an amazing project. It has saved the day numerous times for me when a game doesn’t work with normal Proton.

That’s definitely on the slow end by today’s standards, But then again 10 years ago we only had about 12 Mbit on a bad 20 Mbit connection. 😋 When we moved 9 years ago better internet was a priority, but I think now almost everybody here in Denmark have access to relatively cheap 1Gbit. Relatively cheap being below $100 CAD per month. We pay 439,- kr DKK or $95.- CAD.
If I recall correctly we started out with 300 Mbit here 9n years ago. The price has stayed the same, but the speed has gone up.

With 1 Gbit it should be possible in less than ½ an hour, some times the speed averages less than half when I download from Steam, but still it should be less than an hour. The theoretical time for 100 Gbyte is 13 minutes with a 1 Gbit connection. But with decompression and the installation process, ½ an hour it’s pretty good.

If it takes all night, your connection is probably 100 Mbit (about 2½-5 hours) or slower, or it’s poor speed from the server.
On the up side drive speed and decompression becomes irrelevant from a time perspective.

Proton is made by Valve for playing Windows games on Steam and Steam Deck.
It seems logical that it works best for the platform it was designed for.

https://en.wikipedia.org/wiki/Proton_(software)

Proton is designed for integration into the Steam client as “Steam Play”. It is officially distributed through the client, although third-party forks can be manually installed.

very occasionally it would work flawlessly and all would be astounded,

Absolutely, any semi decent game that was playable, even if it had some glitches, was AMAZING.

You must be misremembering things to the extreme.
Gaming in Linux was utter shit in 2005, and improvements were only crawling forward. When we checked WineHQ for compatibility the average score was bronze “unplayable”.
Although the Play On Linux program helped a lot and came out in 2008, Linux gaming didn’t improve much until after the Steam Client for Linux was released in 2013.

I dual booted Windows the first couple of years where Linux was my main OS, ONLY to be able to play games. After a few years I got tired of dual booting and ditched Windows completely. The result was that I gamed very little, and when I did, it was retro gaming.
Things improved a lot with DXVK, but that did no come out until 2018. Up until then you could almost only play games made with OpenGL, and even that was hit and miss.

I haven’t seen any Proton propaganda, and fortunately a lot of progress on Proton goes back to Wine, so Wine is also a lot better today even without Proton.

So Proton does not deserve all the credit, a lot of work has been done before and outside Proton. But Proton does make it dead easy with the Steam client, but today it may not be necessary if you use other tools to mange the Wine configuration on a per game basis. Or if you are an enthusiast that like to do it manually.

But 21 years ago, even an expert had very little luck except with very few games.

Compared to when I started with Linux 21 years ago, we are absolutely spoiled with games that work well today.