If the range on corkscrew doesnt go up, there's no real reason to max it. I left it at 11 and maxed booster because I hate the idea of putting 3rd job SP into previous job skills, even though it seems everyone does that.

My friend said he was going to max shockwave due to a lack of Dragon Strike (he's a bucc) but I still think sharkwave can replace it since its faster, has better range and isnt stopped by platforms or ground level differences.

As for drain, I prefer Barrage for a single hit move since its MUCH more powerful and you'll be level 100 before you can max drain anyways. The only downside is its speed. At level 105 my Drain is level 5, and I only use it as a pot saver from time to time, but when dealing with larger or stronger mobs (himes or newts for example) it becomes inefficient.