^It doesn't have to be, that's just creative laziness. The actor and/or director should have come up with something about Sybok's personality/mannerisms to distinguish him as still being an alien, and a Vulcan in particular.
On occasions when Spock's emotions were let loose, it always came off as odd and unnerving, IMO. And take a look at TNG's "Sarek"--Patrick Stewart gives us a tour de force performance as Picard channeling Sarek's lifetime of pent-up emotions being unleashed. We have Stewart playing the human Picard displaying emotions, but he's not remotely the same character as Picard.
The concept from TOS was that Vulcans suppressed their emotions for a reason...that they were a very violent and barbaric people. Sybok should have at least given hints of a dark and violent side that he was keeping in check. Some resentment towards Spock might have been an interesting direction to take.
If you're going to give us "the emotional Vulcan" cliche, do something interesting
with it. Don't just put ears on a character who doesn't even have a compelling reason to be Vulcan.