It seems Sora was able to weild the Keyblade because it chose him, the reason I said Ven's story cleans up is because his main reason was being half of a blade that could summon KH. That's really his in story purpose. I was talking about the meta reason he existed.
I still don't see your point... are you trying to say that because the plot of his story is mainly driven by plot devices rather than his personality as a character, he could be substituted by any other character, and it would be the same...?
That's not quite true, because only someone with his type of personality (naive, happy-go-lucky etc) could be pulled along by such plot devices in the first place without it seeming unbelievable.
What is Ven's actual reason for existence in relation to our meta perception of the plot of BBS?
I guess you mean, the plots other than his own...? To drive Terra and Aqua's character development and plot is probably the biggest one.
So what do you want me as the starter of this thread to say? Does Ven really have to exist or not?
The story of birth by sleep, as it is, needs him. Just like the story of days, as it is, needs Xion. It is how it is. The question should probably be, does Birth by Sleep have to exist or not?
The answer depends on your personal beliefs.
No, no video game needs to exist.
No, no game after KH1 needed to exist.
No, no game after KH2 needed to exist.
Yes, this game is important for bringing money in for SE.
Yes, this background is important context for the series.
Yes, this game will be important for KH3.
There would be heaps more answers.
OR, the question could be, does the plot of birth by sleep have to be the way it is? Could it have told a different story?
I am one who believes that the story presented in Days was like something out of a bad fanfiction, and almost any other story that made sense when put to KH1FM, CoM and KH2FM+ would have been better.
The truth is, any story could be written any way as long as the basic canon facts aren't ignored. Same goes for birth by sleep. As long as the rest of the series still made sense, it could have been about pretty much anything.
Whether there is a better story that could have been told or not... that's up to your own opinion.
tl;dr cutting ven out of existing plot = no. a completely different plot for bbs? up to you.