Is there any point at all to ships below battleship class in MoOII? I've played this game extensively, so I figured I would have thought of something by now, but then again, I only learned how useful fighters could be a few months ago. Occasionally I'll use a cruiser to start or prevent an early rush on the enemy, but that's all I've found them good for. Even Battleships become somewhat obsolete after titans are researched. Any thoughts?

I guess carriers might be useful, but only as a distraction. Once you have enough weaponry\shielding on the Titans, nothing can stand against them (well, except the Doom Star).

If you run with a specie that has a bonus to defense, then the destroyers or cruisers can be worth it since they can have such a high defense that they'll never get hit except with missiles, at least in the beginning.
They can also be useful if you need a quick defense force, since battleships take a long time to build.

Otherwise, yes the smaller ship sizes are useless.