I used my Pansear/Simsear up until after the end of the main story, although I never really used him much. On the rare occasion I did use him, he often couldn't take down any more than 1 Pokemon, if that. So, while I was grinding for Cynthia and the E4 (I was seriously underleveled most of the game, so this was quite awhile) the poor old thing could barely get past one Pokemon without going down. Now, he was about ten or more levels below the competition, but the rest of my team could at least take down one Pokemon before going down. So I finally boxed him and went out and caught a Drillbur, which I trained into an Exadrill. I found that not only was this new catch far better than Simsear, but also leveled far quicker, likely for similar reasons.