It's not a bad idea, however I personally think it looks way to much like the current daily challenges. I think it would be way better if the achievements would be a bit more challenging and the rewards would be higher. As I don't think I'll attempt to win 5 games of SkyWars for 150 exp and a cubelet.
It may be better to just make daily and weekly achievements for every game seperately, so for skywars a daily achievement could be to get 5-10 wins. A weekly achievement could be to get 50 wins. The rewards should be a bit high so they're actually worth doing, you might be thinking that players won't play other gamemodes with this, but if the rewards are rewarding enough they'll finish several daily achievements.