Hmm. Just remember that the Empire is a huge fan of standardisation in almost all matters, and that they were preparing for this war for centuries. You're more likely to see a "diverse" Republic fleet, IMO.
True that, but a fleet should still have several different ship classes all the way from huge heavy-hitting battleships to small scout ships. Sending a Star Destroyer on duty that could be handled by a much smaller ship is wasteful, something an Empire should also be mindful of. Not to mention specialized ships for different needs that can handle their area of expertise much better than a standard design meant to do a bit of everything.