In that they at least both have some history with Picard, and the film could've fleshed them out more instead of going with the EVIL CLONE story. Hell, almost any antagonist character shown previously would make a better fit than the psychotic baldie who looks nothing like Picard.

It's vaguely more credible than "everyone's mean to me so I'm gonna kill 'em" - which is about all the "motive" one can attribute to Shinzon - but only vaguely. YMMV.