i think lax in gen 3 is easily more dominant than ttar in gen 2 tbh (definitely historically, but even now).
gsc snorlax is the single most dominant pokemon in any metagame. adv tyranitar is not as good as gsc snorlax. adv tyranitar is only slightly more dominant than rby snorlax. dppt tyranitar is not nearly as dominant as snorlax in rby or gsc, and is maybe more dominant than adv snorlax.
rby snorlax isn't too far behind gsc snorlax as far as dominance.
it's only anywhere near unimportant in dppt, but it's still ou there...
so gen 1 ttar doesn't exist
gen 4 snorlax is ou, so it is naturally considerably more dominant than something that doesn't exist.
as far as relative dominance, to expand on borat's post (with minor, debatable differences)
gen 1 snorlax > gen 4 tyranitar
gen 1 snorlax < or = gen 3 tyranitar (it's probably <, but barely. it's also somewhat skewed i think by the fact that tauros and chansey are so good)
gen 1 snorlax > gen 2 tyranitar (by a lot)
gen 2 snorlax > any tyranitar
gen 3 snorlax > or = gen 2 tyranitar
gen 3 snorlax < or = gen 4 tyranitar
a big part of it is that gen 2 snorlax is better than any tyranitar, but gen 3 tyranitar is only better than gen 4 and 3 snorlax, and gen 1 snorlax is debatable. plus tyranitar doesn't exist in gen 1 so it immediately gets less sway.
zapdos is 2nd best in gsc but it isn't even top 3 in any other metagame, or not even top 5 for that matter... and as for starmie and gengar... how.............
<&spies> FUCK i just SNEEZED and made a MESS