There isn't anything such as "more likely" in theories, people act as if they can predict what the author does, as if there is some logic in what Oda does?
Oda made Shanks lose his arm because his editor told him that it would increase engagement, some people think he planned everything in the story in a straightforward manner and that everything must be "logical"
A theory is a theory, it's a hypothesis in other words (which is a better term)
If someone says that Luffy will die before Elbaf, it's a hypothesis and it can be a theory if it's founded on solid arguments. Is it likely? No but it remains a valid theory/hypothesis until it gets confirmed or rejected
It's like the people assuming that this arc is ending while nothing confirms it yet
I do think it used to be easier, because the scope of each arc was just contained to that particular moment/conflict. Now Oda tries to relate everything to ancient history, and with that a lot of things - characters especially - are just sort of showing up out of nowhere because he doesn't want to/can't take the time to set it up properly.
There seem to be a lot less "two-and-two's" that you can put together nowadays to predict where the story goes, and what characters might do I think, and that makes theories less and less probable. The story doesn't really take the time to resolve a lot of things anymore anyway.
As far as powers are concerned, the rules around haki and devil fruits have just gotten too muddied up to predict anything sensible, and that's not to mention the "Ancient Tech" which has no boundaries at the moment that's now creeping into the story. This arc we have immortal beings teleported away because of a rope with Joy Boy's 800+ year-old haki... I mean, what can you say?
Egghead hasn't ended yet as far as I can tell, there's a lot of loose ends that still need to be tied up, but we'll see.