I was wondering the same thing earlier in my fish keeping days, had mbuna which were crazy all over the tank little guys (my first real fish I had kept); bought some bigger ones at an auction (adult sized, my saulosi were still juvies), and everything went to crap basically. Wasn't satisfied with the tank, sold all my mbuna and started getting into new world.
Got several JDs, decided I'd rather have a GT, so I sold the JDs and got me a GT, assuming he'd be personable...He's grown quite a bit since I got him, but he's still shy of me, had him about half a year now. Every time I walk by the tank he sprints for his cave, sucks man. Went new world for the personality...my mbuna would come to the top of the tank every time I walked by like little puppies, my GT won't. The Firemouth and convict will, but they're only there to keep the GT company and bring something to life in my tank.
Thinkin about goin back to mbuna, even my tang tank (calvus and shellies) greets me when I walk into my bedroom...feelsbadman. Thought I'd have more personality with new world, don't believe all the hype. Unless it takes years...took my saulosi a week to be at the top nippin my fingers thinkin it was food. Jus sayin