I think it undeniably is if Bitcoin is your frame of reference. If it was the only cryptocurrency out there then it would be "the most decentralized" by virtue of that.

I don't think the relative centralization compared to Bitcoin is the weak link there, it's more the fact that every Monero fan I know also owns Bitcoin for obvious reasons.

You can say Bitcoin isn't the best when it comes to particular criteria (and of course I understand the desire for privacy) but it is usually the most logical thing to try and acquire as much of as possible.