Arid Archway is an interesting design that can provide some value, but I suspect that providing only colorless mana, it will end up being too weak to include in most decks
Typal decks like this are generally good for social games, and often struggle at higher brackets
The reason that modal spells are powerful is that they offer flexibility, but because they have at least one (and sometimes more) ability that only works with a specific creature type, the Onslaught charms are much less flexible (and therefore less playable) than most of the other "choose one" spells printed throughout Magic 's history
Players enjoyed the opportunity to get multiple rares, having a guaranteed foil slot, having an opportunity to open a card from The List , getting an art card, etc
While this is worse, always entering untapped is a huge upside, especially for fast or aggressive decks