You missed my point, which is that the poster was complaining those countries would never DOW on Trebizond because they were so far away - but Trebizond invading Corfu is much less believable than Sweden invading Trebizond.
Both strike me as quite unbelievable. Especially if it's all over Corfu.
Trebizond quixotically trying to smash Venice's vassals in a moment of presumable Venetian weakness would be stopped by the action of Western powers.
Genoa or Naples joining in I can buy. England or Castille less likely. Like I said, no one gave much thought to Byzantine annexation of Achaea. When Nicaea annexed Latin Empire, it didn't find itself at war with half of Europe. Few nations also cared to help the Byzanties - local power of Hungary and the Vittorio Amadeo episode are only two cases that come to mind. That, and the French knights at the battle of Nicopolis. But these knights didn't come to Achaea's help.
But it's also quite true that expansionism of the Orthodox powers in the area WAS curtailed repeatedly by threats from larger Catholic powers
Generally true, but not exactly true when considering the post-4th crusade period. The Latin Empire received few support from Europe, and local European powers - Bulgaria, Serbia, Genoa, Venice, not England and France were Byzantine headaches. Point being, early in the game the episodes when a nation at one end of Europe cared much about the events on the other end were few.
And it's not like everyone in Europe loved Venice and was always ready to help it against the dastardly Greek imperial remnants. Just because Milan is an ally of Castille, who's an ally of England, who's an ally of Venice, it doesn't mean that Milan is on Venice' side.
Mind you, Venice should be strong enough to repeal a Trebizond attack on Corfu by itself, unless Trebizond is close to reforming the Byzantine Empire. But in that case, I wouldn't mind a more extensive dogpile on Trebizond. Frankly, Corfu should be a Venetian province from the beginning, and independent cores on Crete and Corfu should be removed, so that they wouldn't be releasable and could only appear as revolters.
My problem with human OPM's is not the ease of their expansion in general, but the fact that a human OPM, surrounded by AI OPM's is like a wolf among sheep.