I'm sure they thought fans would like the nod, but it seems like 90% of people hated it. It was unnecessary and Michelle was fine on her own without that.
That's pretty much sums up my thoughts on the matter.
As many fans have noted, it's somewhat comparable to the John Blake reveal in TDKR, as these name-drops were placed at the tail-end of each film and involve film characters who weren't exact mirrors of their supposed comic book counterparts. However, I'd say that this "MJ" reveal is essentially the inverse of the "Robin John Blake" and it's much less impactful, as it currently stands.
In the case of TDKR, it can at least be said the film itself took the time to build up the John Blake character as someone who idolized Batman, related to Bruce Wayne, and believed in his mission. Bruce was also shown to have taken an interest in Blake and trusted him enough to "let him in" to his world/mission and teach him whatever he could in a short span of time. By the end, after realizing he could no longer operate within the "shackles" of the police force, he was already on the path to become a vigilante when Batman chose to leave him with the necessary tools to take up his mantle. So while not being a complete mirror of the Robin from comic book canon, he was at least shown to be a Robin-like character in more ways than one.
Revealing Blake's true name to be "Robin" in the end was obviously a wink and a nod to the fans in a way, but it was certainly more than that. It drove home the the idea of what Blake represented to Bruce/Batman in the film (orphan, sidekick, etc) and what he was destined to become (heir to the mantle, future protector of Gotham) -- which is obviously the "Robin" connection. This also marked the absolute end to that series of films. And while the name-drop wasn't something that was even necessary in this case, it sort of served as the ultimate "payoff" in terms of how it related to the theme of the Batman legacy continuing on.
In the case of Michelle, she was a bit player in Homecoming. There was nothing in the film that linked her to the MJ of comic book lore on the surface or through her character traits (quite the opposite in many ways), or even in terms of how she fit into the film thematically. Therefore, it didn't really provide any kind of immediate "payoff", which is why it comes off as little more than fan service or an "Easter egg". It's basically just a little tease of what might come later and how she may ultimately fit into the grand scheme of things down the road. (It kind of got an "eyeroll" from me instead of a "Hell yeah!")
So it's obviously not this egregious moment that was in any way detrimental to the film, but it also didn't really add to anything that was presented in the film, which is why I and others have said it felt relatively pointless or unnecessary. It doesn't help that it's likely going to be a few years before we get any kind of payoff to this moment in Homecoming, but I'm sure they'll eventually take this in an interesting and (hopefully) worthwhile direction when all is said and done.
