i think that krocktopia should give you more exp im lvl 28 fire and need more exp
There is nothing wrong with Krok and it's XP. Do more side quests if you want to level up. Honestly, by level 28 I'm out of Krok, into Marleybone, and already done with Wysteria.
I hope you don't mean that you're level 28 and still in Krokotopia. At that level, you could be in Marleybone, possibly even Mooshu, if you avoided the side quests. Anyways, I feel that Krokotopia gives the proper amount of experience for the level range. You aren't going to immediately reach level 95, so you may as well continue questing.
Also, I advise against power leveling in a dungeon because you miss quite a few spells from doing so. For example, let's say you power level to level 48. Sure, you have your rank 7 spell, but you missed the spells given for completing Krokotopia and Marleybone. For Fire, that would be skipping out on Steal Charm and Scald, respectively.