I must be old. I see 1MB speed and think 5MB is damn impressive.

For many many years, I was perfectly happy downloading my GOG games over a 10 Mbit/s cable modem line, which gave me a 1.2 MBytes/sec download speed, or so.

Admittedly games have grown more and more since then, but I think I still had that when e.g. The Witcher 3 was released, which I still consider quite a huge game in size and weight.
An example of a perfect AI response. Basically it is correct in all its vagueness.

I should create an AI which replies to all questions "Anything is possible, except the impossible.". Can't argue with that!

Especially when download speeds in general in the 1990s (obviously GOG did not exist then) were in the Kilobytes and people were using 56k dial-up modems or at best, T1 and ISDN lines.

Bro, when people get old enough to surpass technology.....it is a little depressing. The flip side of this coin is being in the grave. Thus I try and keep my spirit up with more positive things like, cooking.

It is interesting to see something become obsolete though. Like how old video games were made years ago, to have better mechanics. Now in 2025 developers claim they cannot reproduce those mechanics in modern games. Just watched a youtube video comparing old and modern gaming. Full of irony.

This is a perfect example when it's better to talk with AI than waste time arguing with a headless troll to maintain harmony.
I should add vagueness to the great feeling of remaining silent from now on. It could keep arguing forever with that~

About download speeds, broadband has been the norm to me since the beggining. I wish I could comment.

As I stated, I think you can narrow down the cause and be definitive, and I gave my reasoning.

I'd agree with you in other circumstances, but not this one. If you disagree with me, then take apart my reasoning.

1. Definitely not ISP based ... too many ISPs are involved.
2. Definitely not route ... too many different ones are involved.
3. For many of us, probably most, this slowdown happened overnight, and has stayed that way.
4. Even if Fastly CDN is causing the slowdown, GOG have kept using them.
5. Fastly CDN might be acting on GOG's instruction, or GOG are only prepared to pay for hosting on a minimal number of servers now, which would explain why many, probably most, still get a good download speed with GOG.
6. The decrease in download speed is a set value, not a percentage, which tells us it is deliberate. The only time it varies, is when the GOG site is really busy, and it slows down even worse, sometimes to a crawl of 200 Kilobytes a second or less. Immediately after that CDN crash back in mid 2023, for around a week, my download speed was around 104 Kilobytes a second ... totally abysmal.
7. All of those impacted, have continually had good download speeds with other sites during this period. Many of them too, probably use Fastly CDN.

So for my money, GOG are at fault, probably due to cost saving or are attempting to coerce the use of Galaxy.

If Fastly CDN are to blame, why have GOG continued to use them?
Download speed for those impacted after the crash in 2023, was fine before then.