KeoniBoy: Since we do NO DL from GOG, Epic, or Steam on our browser, we can't speak to that issue.
Who is this "we"? All GOG users, or is it more like a "royal we" as Jeffrey Lebowski puts it so eloquently?
In case you didn't know, you can also download GOG offline installers with a web browser, without the use of the Galaxy client. That is what the OP in this thread is talking about.
Here are my test results (not recent, but long after these issues were being reported already, and I haven't seen it go worse since then). As you can see, for me Steam was considerably slower than Galaxy or the other gaming clients, but I still consider Steam "fast enough" as well:
Download speeds:
GOG offline installer with the Edge browser: (Biomutant) 24 MBytes/s (yesterday I actually got a better download speed, around 38 MBytes/s; this seems to vary somewhat, probably based on busy hours, maybe even which game you are downloading)
GOG Galaxy offline installer download: (Biomutant) 70 MBytes/s
GOG Galaxy: (Biomutant) maybe 55 MBytes/s on the average (fluctuated a lot between 20-65 MBytes/s, sometimes stabilizing for a longer time to 55 or so)
Steam: (Resident Evil 5) 37 MBytes/s on the average (peak: 40 Mbytes/s)
Epic Games Store: (GTA V) 70 MBytes/s on the average
Ubisoft Connect: (Watch Dogs) 60 MBytes/s on the average
EA: (Dead Space 3) 69 MBytes/s