Is Sephiroth actually Jenova?

[The Crystal]

I seem to be fighting a losing battle trying to convince people that Rinoa=Ultimecia=Zell=Squall=Big black guy.. is just overanalysing.. or one step beyond that.

It's "one step beyond that". The Ultimania already destroyed this theory, by stating that sorceresses have normal life-spams.
These people aren't overanalysing, they are directly contradicting official information.

People who still believe Rinoa is Ultimecia, are the same as people who believe Jenova was controling Sephiroth. They refuse to accept reality.