Shouldn’t Mikey be top dog due to the last Ronin storyline?
Also, in most mediums, Mikey has always best Ralph when he’s even remotely serious. The best example being 2000’s series when Mikey casually beat Ralph in that universal tournament without even trying.
Even further, Splinter even claimed Mikey has the most potential. The only reason he’s not above the other 3 is because he lacks focus and he doesn’t care to train as hard as Leo and Ralph.
haven't been keeping up with TMNT, so I don't know.
His average mindset doesn't enable him to be as vicious as Raph and he's often portrayed as being beneath both Leo and Raph. If we're using examples, the 2011 TMNT show had Raph and Leo easily destroy Mikey and Donny. Also, the only reason why Mikey won that fight was because he used banter to throw Raph off his game. That's not quite the same thing as definitively being a better fighter.
A characters potential doesn't matter if they haven't trained. Until Mikey trains to the point where he can definitively beat Leo and Raph, I'm not going to take conjecture about how awesome he COULD be at face value.