There are two really good things about the Epic store and one thing that might be good or bad long term:
1.) It's a major platform (as in has AAA games) pushing a better revenue split for developers. I thank GameJolt and Itch for starting this, and I am glad to see Epic taking it seriously too
2.) The financial support for some developers to give them a certain amount of money to develop and launch their games exclusively on Epic (matching or exceeding the expected sales they would've got)
3.) Giving developers money to release their games for free
Point 1 is already something Itch does. The only thing that could improve is exactly what you're saying, a few serious, bigger games. Not necessarily AAA. But then again, stuff like Celeste is on here, so they already kind of do it in terms of the big Indie games.
Point 2 I don't see as something that Itch could afford. Really only comes from Epic's success with Fortnite and investments. Maybe there's a crowdsourcing angle that could be exploited? Although I feel Patreon already handles this well enough
Point 3 is yet to be determined if it'll be good (could distort the market even more :S), and also ties into Point 2 in terms of me not sure if Itch could afford it.
But I am glad that we are seeing some improvements for the smaller devs out there, thanks to these platforms. I do think you're onto something with bigger game releases.