Yeah, I agree. Like I said earlier, the moment you try thinking about it too hard and adding more backstory, it falls apart. The Turtles were pure 80's and the mutation is about the extent that we really need to know. Pushing that further is just a bad idea. Some things are just better left alone.
One of my favourite Turtles movie was actually the animated movie from awhile back. I'm not talking about the CGI movie, but rather traditional animation, which featured a crossover between all the different versions of the Turtles including the comics. It showed that the 80's Turtles had way more personality than the ones from the recent cartoons.