Yeah, Grass in general is pretty awful defensively too. At least it has a few more resistances though. Exeggutor is one of my favourites from Gen I, and its typing never really seemed to cause it to be at too much of a disadvantage. I had Aurorus on my team in Y for a while though and it was pretty dire haha.
Mawile is a dream to use competitively. Smogon should really consider banning it from the OU, or at least banning Mawilite. Such incredible defences combined with the insane attack Huge Power gives it really shouldn't be allowed :P Surprisingly i rarely encounter opponents that use it though.