Did you completely miss what I said about definitions? Define "stronger" first.

If you define it as brute strength (who can lift the most), then who knows. Probably Sephiroth, but there's nothing definite. If you include magical powers in the definition, then definitely Sephiroth. If you define it as "better fighter," then there's a good argument for Cloud, considering Cloud does defeat Sephiroth.

You seem to just be looking for evidence to justify a desire for Sephiroth to be "stronger." And there are legitimate arguments to be made, depending on your definition. But don't pretend it's a universal fact, especially when you're just using vague, undefined terms.