Is Flash Sentry's Major Flaw Really The Issue?

Okay over a year ago (I think) I made a blog asking how Flash Sentry, or Brad in some people's case, was a Gary Stu. And after some time and hearing other people's reasons, I now understand how. A nice guy and a slight dork are his only traits. He doesn't have much of a personality so he doesn't have cons as much as he has pros. He's a walking middle ground. So what this leads up to is, why do people want to instantly despise him because of that? Many reviewers including the famous brony analysts state the same reason, and some can't find a reason to hate nor like him, though there is one common thing that all of them tend to leave out when stating that reason, isn't that the same case with many of the background characters or one offs we've come to love in an instant? How many of us can even remember the reason we liked background characters before they became a big thing? I mean Lyra, BonBon, Derpy, Vinyl, all of were as implied, background characters, Just ponies with no lines, no established personalities, only there to take up empty space. Yet here we are treating said characters as if they were our own children. In fact, it sounds even more contradictory when you realize that we were the ones who made their personalities for them, and that's how we've come to love them so. Now if Flash is in the same category as them, why is it that we take the route of disliking him? He hasn't hurt anybody as of now, only exist. If I may guess, it's more on the lines of them thinking he's useless as a character. The background characters at least did their job of being in the background. What I mean is, Flash was supposed to be a big deal, he's the established love interest, and after years of watching Disney movies, that's kind of important. A love interest is not supposed to just be there to exist, he supposed the lover, friend, partner, and companion to the female or male lead. They are there to help them any chance they get as well a develop a relationship while doing so. Heck, even Eric from Little Mermaid did his part by killing Ursala. And then we have Flash, a love interest is what he is, and yet he doesn't fulfill that purpose right, it just ends up as more of a mutual crush and nothing more, hence why they think he's useless. He had a role and he didn't live up to it, for three movies straight. This, I think, is what ticked people off deep inside, and found themselves to be annoyed, which lead to loathing him. This is not his fault, it's that the writers can't seem to find the time to do something with him, which shouldn't be a big issue, because look at how much time and attention they give to the fan favorite characters lately in episodes. I'm sure they could think of something if they actually tried. Back to the point the point. From what I see it's not just the issue the he's underdeveloped, rather he just doesn't do anything for an established character. It's like a rc car with no batteries, it just sits there and goes nowhere so you just get bored and ignore it, but if you put batteries in it, you'd like it and have a lot more fun with it. So personality wise, I think he's just fine. If you want him to be fixed, just give him more screen time ,interaction with other characters, and let him do something. So what do you say, am I close? If not tell if I'm wrong and add your two cents. I just like talking about this issue and more mad at the writers than him.