Cruisers will still hit rat frigates just fine. You lose some damage, but it’s not like a battleship trying to shoot rats that are up on them. That’s why destroyers are optimal, though: they can hit and apply damage just fine to frigate or cruiser.
Xeux also gives more good advice. If you do decide to go with a cruiser for doing Lvl 2’s, make sure to put a prop mod of some sort on there. If you find you -do- have trouble hitting the frigates, turn it on, pull some distance, and then blat them. I’m also assuming you’re looking at flying a turret bearing ship. If you go missiles or drones, then application of damage to frigates is not an issue at all.