I’m sorry, but no, Miguel is anything but useless. Even in auto-mode in Arena, he functions very well in a variety of comps.
He has the highest HP growth out of any Support hero (including Alice before growing Enormous). His healing is based on his basic attack, which is further enhanced by Jessie’s Disk. His Skill Power needs no improvement either since he has a passive that enhances that on his own.
Theory-crafting time:
How does one fit a hero like Miguel in a team? He is a purely utilitarian hero who contributes through enhancing team performance and zero direct damage. As such, a player can get away with 4 hyper-offensive teammates because Miguel’s playstyle enables exactly that. Is he perfect as a Support hero? Of course not. He particularly works well with competent peelers to get divers off of him. Hero’s like Tia, WALL-E, and Finnick have skills that pushes enemies away from Miguel and keep the backline protected. As long as he has such allies, Miguel can continue to do his job.
Usage Theory:
Miguel is unique in that he is not that suited for a defense team. He is particularly good in a comp a player would manually set up to attack a defending Arena team because the rest of his teammates are also cherry-picked to deal with a known defense. Miguel is also 1-star hero, and as such suffers the same issue as other 1-star heroes. It takes FOREVER to get them to max stars! And so, it’s impractical to have him try to keep up competitively to be part of a defense team. There’s also the fact that Miguel was released all the way back in October. Offers to buy his hero chips or earn them through contests has long since passed. He’s also not a particularly popular character when compared to the rest of the cast. No matter how successful the movie Coco May have been, it can’t quite compare to franchises that have earned greater sentimental value towards fans. He also can’t hope to compete in a popularity against even some of the newer characters like Elsa. Recently, they’ve also released 90’s characters such as Darkwing, Herc, and Meg, as well the classic characters from Alice in Wonderland.
I guess all I’m really saying is that Miguel’s a unique case. You have to acknowledge that his skill set is by no means, weak. Because objectively speaking, Miguel is a very strong hero. What’s working against him in terms of usage is the timing of his existence. Miguel is not yet a pop culture staple. Older servers have a lot of players who are sentimental, so Miguel is probably not the hero they’d think about first. As for newer servers who only recently had him added, their opportunities to build him up into a strong character is just not abundant.