groudon is ground type, and the types it is weak to are specially inclined (water, ice, and grass), while also having drought weakens one of those weaknesses so basically, it's only weak to grass and ice types. and i'm fairly certain that groudon has some actual special bulk to back up his awesome physical bulk as well
avalugg is weak to steel, rock, fighting, and fire. 3 of those types are physically inclined while fire is more specially inclined. fighting and fire are among two of the most common attack types in OU, steel is on the most popular OU poke the past 2 generations, and there's stealth rock
while numbers alone will show avalugg has a better defensive rating than groudon, his typing makes him much worse at taking hits especially when it will be common for him to come out with only 75% of his health, also having no resists outside of ice attacks is pretty shitty
avalugg is weak to steel, rock, fighting, and fire. 3 of those types are physically inclined while fire is more specially inclined. fighting and fire are among two of the most common attack types in OU, steel is on the most popular OU poke the past 2 generations, and there's stealth rock
while numbers alone will show avalugg has a better defensive rating than groudon, his typing makes him much worse at taking hits especially when it will be common for him to come out with only 75% of his health, also having no resists outside of ice attacks is pretty shitty