those teams will not remain good forever, no. the strongest correlation to success will be their market sizes.
with a big budget, they can be consistently better than other teams, for sure. that's a stacked division as far as budgets go. fwiw, the unbalanced schedule isn't so large that you can't make up for it by beating up other teams in the AL.
in general, if one division is realyl strong, there's likely a weak one out there somewhere... hopefully not in the NL,
what's guaranteed every years is the the league has a .500 average LoL