Yes because it is a divergence from the current bitcoin so would mean it is an alternative version of bitcoin so altcoin it is, regardless if more people support it and it becomes the leader it is still an altcoin, in my eyes anyway.
this has somewhat fazed me as well... the original bitcoin didn't have segwit and didn't have larger blocks, so, the bitcoin running now, which has segwit, and the forked one - bitcoin cash, whose blocksize was increased, are both modifications of the original.
so that means the original bitcoin is gone (?) 
It really doesn't matter. Whatever name, they are what they are. It's like discussing if Devian Linux or Slackware Linux is true GNU-linux. Sure, 100 times more devian users, but both are linux. And then there are distros that go against so many of linux principles, that most regard them as not being linux. The difference here is that Bitcoin = money (currency or asset). So instead of "whatever suits you best", there's an interest in protecting the "market share".
Nobody, not this "Core" group can claim to be more Bitcoin that the original Bitcoin. And as you say, what we have today are siblings and variants. Most variants will be worth $0. But if some variant holds value, it likely serves a purpose, just like a distribution does. And that's all that matters.