You may or may not be forgotten … but I don’t see the problem the way you see it.
The group I think you are talking about would be players who don’t have TC20 yet or haven’t run it long enough to have a selection of 5* heroes. (Assuming those players haven’t spent a ton of money summoning heroes, that is)
I’m well beyond that now, but here’s what I remember from my roster at that point and players who were well matched with me:
I had a really uneven selection of heroes by color (Classes didn’t exist then.)
And my uneven selection wasn’t influenced by which heroes were out there including event and atlantis 4*\s, or even which 4* heroes existed from TC20.
My selection was uneven because randomly pulled heroes are very unlikely to have an even distribution, and most players start out with some sort of mismatch or other. Some of the fun of this game is figuring out how make a roster work for you when it isn’t even.
In my case, there were a few colors I was short in, and I was very short of hitters, and had more healers than I knew what to do with. A problem–not really, but uneven and interesting? YES.
And no matter what … once you’ve played long enough, you collect enough 4*s to round out your collection and start to get some 5* heroes. If you play free or cheap, you will spend more time getting there. If you summon a lot of heroes, you will get there faster. But either way you will get past it.