Good point. It's true that Tear has the highest possible activation rate (that is, 50% with Naesala at max SPD - granted, that's at 36, but all the same). Even base Naesala has better activation rate than any beorc unit, even if it's only by 2%. And yes, it OHKO's red dragons (Hard Mode):
Base Tibarn (hopefully by 4-E-3 he has at least a few levels, but I'll leave him at base) vs Red Dragon on a cover
[36 * 3 + 20] - 47
= 81, OHKO.
I never use laguz so I don't know a reasonable level for Ulki or Janaff or I guess Vika (all of whom break the 20 SPD cap). But it looks like they could probably pull it off if said dragon wasn't on a cover and possibly if it was.
Base Naesala leaves them with something like 4-5 HP and he's doubling so he at least ORKOs (as do all hawks and ravens).
This is definitely a big advantage for Tear.
Rend doesn't get any bonuses in terms of activation rate, but yes it's been established that it is indeed the strongest skill in the game (although now that Tear can OHKO red dragons, I don't really see the benefits). Perhaps Tear's superior activation rate is enough to put it in the top spot.