That and before Acrobat, Flying in general had pretty bad moves (barring Brave Bird limited to Skarmory, Honchkrow, and Staraptor, of which only Skarmory was definite OU and Honckrow/Staraptor failed because of crappy defenses and "Stealth Rock"). I mean, outside of the very limited Brave Bird, you have two turn moves Fly/Bounce (yeah, good luck with that, obviously you could take advantage of those a mile away, although at least Bounce had a 30% of paralysis which would suck for the opponent), Drill Peck (also limited), Air Slash and Air Cutter. Yeah, not very great moves and most birds either had bad attack, bad defenses, or both which despite their great speed, didn't put them at the top. (Swellow is pretty good but needs Guts to even reach a decent attack score and Staraptor is phenomenal but still weak defenses and could be outrun).
The best birds until now have always been Flying/Dragon, Flying/Electric, and Gyrados. But it was not because of the attacking potential of the flying, but from the defensive side.
Tornelos continues the tradition of bleh defenses but they can work, especially since unlike previous attempts, he has amazing speed faster than 110 which is a big deal as well as aweinspiring attacking stats and awesome stabs to actually use on both sides, a 120 special and 110 physical flying with no negative side effect (unless you count 70% accuracy in normal weather or not being able to use Life Orb a crippling side effect).
As a Specs/Mixed/Physical attacker, he seems scarier than Thundurus since few resist Flying and no immunites unlike Thunder which you don't want to lock in Specs and very little can safely switch in on Tornelos while slightly more can do Thundurus. I like using Thundurus for the ability to use Priority Thunderwaves to prevent unfortunate Shell Smash/Dragon Dance/etc sweeps as well as to break other Thundurus or anything fast without an immunity. Tornelos seems more the attacking type and actually is trickier since it has the potential of more sets from special/physical/mixed/Rain Team support/TailWind/etc.