I'd never heard of this channel, and I'm very wary of strange YouTubers...but this was pretty good.
It lays out a compelling narrative for how this may have been an unplanned exit for Ncuti, with a very plausible-sounding explanation of "he wasn't willing to wait around while they sort out when season 3 will happen." I do hope the truth comes out in short order - I'd rather not put up with the equivalent of two decades of speculation over what went down with Christopher Eccleston.
I do think there's a third option amongst the narratives, too - it may have been "always the plan" in the sense that Ncuti had a 2-season contract, but that he had planned on renewing until all the waiting started to interfere with him picking up new projects.
Oh.