review the pix.. and not the really huge leaves are grown in conservatories and green houses ... i suspect you will never duplicate perfect growing conditions in your house ..

https://duckduckgo.com/?t=ffcm&q=Philodendron+Melanocrysum&iax=images&ia=images&iai=https%3A%2F%2Fi.pinimg.com%2Foriginals%2F6b%2Fc7%2F53%2F6bc753ad3245ee6f2aca6ed7361d25bb.jpg

that said ... what would you do with a huge plant.. lol .. one of those.. fear your success plants .. lol ..

the injured leaf looks like what we would call mechanical injury.. meaning it was physically abused .. as compared to bug or disease.. nothing you can do about it except cut it off eventually ... as long as its green.. its converting light to energy ..... and you dont have a lot of leaves for such.. so dont cut it off too soon ...

and im sure you dont stand there all the time with the plant in the air.. lol .. how about some info on its location.. light.. etc ... or even a pic of where it usually stands ...

on some level.. i think you have a babe plant.. and its only failure so far.. is its not growing as fast as you want ... be patient.. perfect cultural variables.. water.. light.. etc ... and see what happens ..

and no.. you dont cut off leaves to make other leaves larger ... and again.. in your case.. you dont have enough leaves to be sacrificing them ...

ken