Why would they change Roman UD, which require throwing away art asset and make new art, England rework they just changed the UA of the civ which did not require making new art or throwing away old art. If they want to give Rome Another leader there is much easier option than a Byzantine emperor to pick from anyway.
It's one asset, not a whole civ. I don't know where the line is for "too much effort," but it's of an ambiguous size with respect to whether it is worth considering.
I'm not sure what the influence thing have to do with anything, Alexander success was based Heavy upon the work of his father and the skills of the people that was with him and also the empire he created was basically a precreation since it is basically the Persian empire + his fathers empire and after his Death the empire broke apart into smaller states. The persian Empire was also built upon previous empires like Babylonian Empire which in turn was built upon Assyrian Empire.
I think you completely missed my point, though. Nearly all empires piggyback on the infrastructure of the cultures they conquer. Pretty much none of them existed for the sake of a single person. The closest examples in history would be equally short-lived-yet-massive conquests that died with their leaders, such as Tamerlane, Napoleon, Bolivar. However France existed long before and long after Napoleon, and the French empire was never so entwined with a cult of personality as to rename cities after him. Bolivar's legacy is quite similar to Alexander's; he has a whole country named after him. And, similarly, we likely would not have had any Colombian civ in VI but for Bolivar's massive regional impact as an individual.
My point is, Alexander's inclusion has practically nothing to do with Greece. Many other "big name" leaders have been swapped out for other civs (Napoleon, Elizabeth, Bismarck, Catherine) and they haven't been missed as absolute "must-haves", nor attempted to be justified by splitting them off into separate civs. They were not big enough as individuals to the point that they manufactured an entire empire, more or less defined differently from predecessors and succeessors, simply around their existence as a figurehead. Alexander would not have been included on top of new Greek leaders if he had not had such a disproportionately HUGE effect as an individual. Alexander is the
only reason we have Macedon on top of Greece, and if by counterexample a figure as large as Alexander had never existed, we would be nodding our heads that Gorgo and Pericles were enough to represent Greece. Hell, we still could be because they are perfectly fine Greek leaders, but Alexander's effect was so weirdly unique that the devs still saw fit to manufacture a Macedonian civ just to include him.
So, again, the analogy is flawed, because we have a Greek/Macedonian distinction in VI purely because of this bizarre, massive cult of personality that was Alexander, a person which doesn't adequately fit into representing Greece but was also so exceptional and influential as to merit consideration of breaking off a Macedonian concept from Greece.
There is no Byzantine equivalent of Alexander. While there may be other justifications to include Byzantium on other merits, my point is that using Greece/Macedon as precedent is, point blank, an awful argument.
(One could argue Constantine naming Constantinople after himself somewhat parallels Alexander, but the cult of personality wasn't as huge nor was the empire mostly coextant with Constantine's lifetime. And at any rate, choosing Constantine would kind of undermine the point of including Byzantium for the sake of having late Byzantine flavor.)
EDIT: In fact, Macedon/Greece actually supports blobbing Byzantium with Rome. A common pedantic criticism about Alexander leading Greece in past iterations was that he wasn't actually Greek but Macedonian. The splitting off of Macedon effectively corrects this slight historical misrepresentation. Guess what another common criticism is with respect to Byzantium? That it was wholly contiguous with Rome and was known contemporaneously as "Rome," not "Byzantium." It might be a misconception the devs would consider important enough to do something about.