Yeah, I did the same and switched to 7 after a while as well. The drop rate doesn't seem to be high enough on 10 to balance out the extra time and SOT being spent on it.
I've been leveling the Cannoneer a bit, and his basic seems to hit pretty decent, but the special is super weak. Then again it looks like the damage goes up a bunch on the special with skill shards, and not at all on the basic. It'll be interesting to see what he's like fully maxed with Chance + Fate sets.