Orcas are definitely top dogs. I think the only animal that isn’t helpless is sperm whales who still have to group up and tail whip them to go away.
They are top dogs, but they are also contested in their own right:
- Humpbacks have frequently been known to group up and interfere with orca hunts , with 2 humpbacks aggressively standing off against up to 5 orcas.
It's suggested that humpbacks in general are effectively invulnerable to orca predation as adults; there was a Bremer Bay video where two whole pods of orca failed to take down a juvenile male.
- Sperms are powerful too; the only case involving casualties that I know of is where the orcas had a numerical advantage and the sperm whales were very passive and possibly subadult.
Bear in mind, these were females. Adult bull sperm whales actively live in colder latitudes where killers are more common, have never been taken yet, and on very VERY rare occasions have been known to chase them away.
- Right whales have been known to efficiently defend themselves against orcas. Sironi et al mentioned two cases where they stunned orcas with their tails and even sent one flying
- Pilot whales have been known to chase off orca with greater numbers.
I think the main way orcas are overrated is that people will often say that a pod of 5 or 6 is enough to take down a megalodon in hypotheticals, because they have been known to kill large whales.
I'm no Meg fanboy but IMO this is ridiculous. AFAIK it usually takes 30+ orcas, upto 70 sometimes to take down even juvenile blue and fin whales, which are flight type species that rarely fight back.
A meg is a completely different story being nearly as big and far more well armed. Orcas taking down even great whites is rare, and the killers usually have a HUGE size advantages over their victims.