Counter-Counter point:
Just because Joker was fighter 1 means very little, because we can assume they had all 5 characters planned for Pass 1 by that point, SNK didn't just approach them after Joker to say they'd like Terry in, they had all the characters locked in by then, considering Steve, and Sephiroth, they seemed to have been in talks for even more before Pass 1 was even a thing.
Sure they had all of pass 1 locked, but Pass 2 probably not. In fact maybe the 6th fighter on the pass was never planned and could be filled by Sega after a request. After all they delayed Brawl to add Sonic, it’s entirely possible they added an extra slot to give another company something if negotiations were going back and forth and undecided before then.
Also where is this Sephiroth talk coming from? I haven’t seen anything on it, and considering Sakurai implied it was A challenge just to get Cloud, I don’t think he would go into meetings again for years right away to get Sephiroth.
Could be wrong, but the fact Hero came first and we know had been in the works for quite some time, tells me that they probably wanted Hero first, then for this pass he said let’s try to save final fantasy.
Also just because one character was planned for years doesn’t mean the others all were