Why would they sink $100 million into a minor league team to feed them?
If MCFC want to call NYCFC their farm team, I don't think it'd be much of an insult. Heck, I'd take it as a compliment.
If MCFC want to give $100 million to MLS for any reason at all, it's a win for MLS and soccer in America.
If MCFC sends over loanees from England or Europe or South America to play for MLS, that will increase the quality of play in MLS.
If an American kid gets signed to NYCFC, then he might be thinking,
if I play well, I might have a shot at the big stage (and big money) with MCFC in the Premier League (and MLS will get more $$$ for the transfer). That's another win for MLS.
And if MCFC can market NYCFC as the place to watch the next great (probably homegrown) soccer player, then that'll be great for attendance for NYCFC and exposure for MLS.