I train at the Skele MD right now and I don't yet have a decent level of Torpedo. It would help, but I'm pumping Air Strike instead. When you 2hko Skeles, you don't need a mob skill that badly. When I come across mobs they tend to be on either side of me rather than in a line I can Torpedo.
I take the 2nd platform from the top and can usually clear out the spawn. When my ship breaks it does suck, but it doesn't break often and I can drop to the mini platforms below and spam FT/Ice and Air Strike to clear out really bad mobs.
Bottom Line: You can train with max Cannon only. Torpedo and Air Strike help speed things up but it's not going to be like you can't train without them.
I take the 2nd platform from the top and can usually clear out the spawn. When my ship breaks it does suck, but it doesn't break often and I can drop to the mini platforms below and spam FT/Ice and Air Strike to clear out really bad mobs.
Bottom Line: You can train with max Cannon only. Torpedo and Air Strike help speed things up but it's not going to be like you can't train without them.