Dude, I hold the sedevacantist position.
Very well, then, do tell me, outside of Thuc's line who exactly has a valid line of ordination? If I recall correctly, the CMRI's line of bishops comes from Thuc's. By denying him, you are denying that the CMRI has valid priests.
Who does, then?
From what I recall, there is no one with a more credible line of succession than Thuc's. Considering how flimsy the arguments used against Thuc's are, if we use the same "rigorous" standards you use, there is no valid line at all.
According to your arguments, if any bishop in the history of the Church ordained someone who later fell into heresy, all of his previous ordinations are dubious. So, during the arianist heresy, most of the bishops had "dubious" ordinations.