RBNY does plenty of youth soccer work across both states including very prominently in the Lower East Side every year, and in any case, the average new nycfc fan has no idea about that kind of work being done by either club.

NYCFC has been a huge marketing success so far for three reasons:

1. they launched a really sharp brand identity right after a World Cup,
2. they are associated with two other clubs that hold cultural cache with two important groups: soccer fans who already respect English soccer and the DPs they brought over and Yankees fans who are willing/excited to check out soccer in familiar environs,
3. and most importantly, NYCFC wasn't burdened by the residual 90s MLS brand association. you see this across the entire league: original, and even successful on the field franchises haven't caught on in the same way as teams such as Toronto, Seattle, Portland, Vancouver, or even Montreal, who were able to enter into their sports market post-Beckham, when the league was more respected, millions of American kids had finally started watching the world cups and playing FIFA, and the sport as a whole was no longer viewed as similarly to arena football.

What is definitely certain pertaining to number three, is that the Red Bulls botched this opportunity to rebrand to catch more of the city, I won't say otherwise. but it's not just because the stadium is in New Jersey, it's because they failed to overcome these branding factors successfully, like SKC did with aplomb. hell, they barely even promoted the team at all, not to mention within the city. City is actively discovering that building a stadium inside the city limits isn't as easily done as said. They have, however, discovered that if you partner with the Yankees and make a Times Square tour bus brochure your media guide, that people will love it. I'm very curious to see how this transfers over when city finally gets its own stadium that will inevitably be further out than Yankee Stadium, and perhaps as intimidating as even the gasp PATH train.

and the idea that the Red Bulls should look to the Cosmos is laughable, since their obstinance in negotiating has actively kept them in the second division, when they by all means could have been the second New York franchise themselves if they had accepted the same parity terms that even Sheikh Mansour found palatable. and in any case, slowly moving to build an okay stadium out in Belmont is in no way more ambitious than actually building a world-class stadium in Harrison.

tl;dr a team with a stadium in Harrison, New Jersey can compete to be a New York local team if it gets its branding more in order, and continues to have a couple of winning seasons while City is still homeless and the Yankees association becomes less strong

edit: format