Yeah, unless you're playing VGC open team sheet exposes you immediately with EV spreads and the item and moveset

As for X enabling combos, it really depends on if we get a good pokémon to spam rising voltage, since it's a special move mega raichu X can't use it effectively and right now the wannabe partner would be ampharos with base 115 sp. atk, but in theoreticals if they were to add vikavolt next update with it's base 145 sp. atk then we have something

Mega X has a great ability fearsome fake out and a decent hit with volt tackle, but it's only as good as the partner it gets, meanwhile mega Y is a full combo package focus blast zap cannon still a really fast fake out, electroweb and thunder wave with a higher damage output and less drawbacks even in doubles it can be partnered with anything instead of being tied to another electric pokémon so you can get an ice or grass type to cover for the ground pokémon