Unfortunate but not the end of the world.
For Doom Marvel's got The High Evolutionary, Osborn, Real Mandarin and Zemo (who's pending)
MCU is still yet to introduce Modoc, Taskmaster, Skrulls, Savage land inhabitants, Cancer-verse (GoTG maybe)
And a decent fill in for Galactus would be Planet Ego. Give him some upgraded minions/heralds and most would be fine with that.
After thinking about it I really don't care about Kang. The only reason people are worried is because Fox has him and won't likely ever use him. But it's Marvel after all and it's not like they can't make new ones that Fox can't touch.