None of the other three are likely to see any use.
STR Chopper's special lets you tear through high-defense mobs, and acts as a minor damage boost against medium-defense enemies. In the few places where Chore Boy Helmeppo is used, such as Alvida, Chopper can usually be subbed if the rest of the crew is beefy enough.
Every so often there's a place to leverage his skill to make the game easier. For example, if a bunch of the high-defense STR pirates on Stage 9 of Expert Khalifa come in 1 round AT, I can use Chopper and not worry about dropping combo and getting hit. Alternatively, I can save him until stage 10, and kill Khalifa a little faster. Works nice with M.Chopper/Blamenco lead.
I'll agree though, QCK and PSY are pretty sad. QCK should have had a huge attack stat, PSY should have had huge attack and HP.
I have a crazy theory, that the way the OPTC devs will handle the timeskip is by adding an additional evolution to the v1 Strawhat pirates, and that third-evolution 5* QCK and PSY Chopper are going to be must-haves like GP Usopp. It would be a fantastic turnaround, a real kick in the teeth to the players that ditched Chopper evolutions they didn't like.
Mirage Nami is used for Zephyr, Knuckle Ensign for Khalifa, and Sengoku makes a bunch of mid-tier units useful. The devs seem to really like throwing the min-maxers a curveball from time to time, which is one of the things I like about this game.
