Kovalev does the same thing Foster did. A brutal KO. Tiger was durable but against hard punching and talented LH's he was overmatched.
Kovalev is too big and powerful for Tiger, but this doesn't end the same way as Foster-Tiger. Foster is arguably the biggest P4P puncher in history. Personally, I'd say it's between him and Jackson as the two biggest P4P punchers that ever lived. Kovalev would beat Tiger up, but he wouldn't ice him with one punch the way Foster did.
Eduardo Lausse a middle from the 1950's, fits in there with Foster and Jackson for P4P punching power. You are probably right about Kovalev not scoring KO with one punch but he would stop Tiger in a pretty one sided affair.