Is this supposed to be normal? I got new internet yesterday, 25 MB/s up and down and it works on Steam - it's even downloading at 30 MB/s sometimes. But in Heroic it's capped at 0.5 MB/s and sometimes goes up to 10-15 MB/s for half a second then down again. What do you think causes this? Lutris is somewhat more consistent, with 2-4 MB/s always.

There are so many factors determining what Internet speed you see that we cannot possibly be your tech support even if we wanted to.

you're not confusing bytes and bits, are you?