The fact that he was able to build up enough AP to use his lvl 3 is completely urs and whoever else's fault. He builds AP like a snail after the patch. Yes it may go on longer than others and it may be a pain but he deserves it for being good enough to build the meter.
Yeah...his AP gain is the WORST in game. Other characters can easily get a level 3 and a level 2 out before the 3 minutes are up- but Sackboy can only get a level 3 and nothing else now................ maybe a level 1 if he's lucky.
I almost always get 5 kills with his level 3 super, on pretty much every stage, even if my opponents are spread out. I usually get 6. You can use his teleporter, bounce pad jump, and grappling hook to get around. I have NEVER gotten 8 kills with it, although I can get 7 in rare circumstances.
Still, he gains slowly. If my opponents are good, I usually don't get my level 3 until the last 10 seconds of the match. So, that one level 3 is the only super I use during the match.
And yeah, I do use his cake a lot, but mainly because his other moves are really unsafe or situational. You can't get to level 3 using cake alone, though, because eventually you're opponents are going to come after you, and you better know what you're doing when they do.
I used to mash X to attempt to get away since I thought I was vulnerable anyway, but it turns out this isn't the case, and if you don't press anything his super doesn't last long enough to kill you 3 times.