I'm personally surprised how much I enjoy their roles as "romantic rivals".
I think it's because they don't act as obstacles or excuses to extend the story, quite opposite in fact since their existence pushes the plot forward and forces the main couple to sort their shit out, Amamiya in particular.
I agree, at least when it comes to Hidesuke. Maya never shows any attraction to him and has even turned him down once already. She's only letting him still entertain the idea of being together because he promises stability. Which makes sense for her character. Maya's conflict here is of "love vs stability", and her journey will be whether or not she can accept Michiru's change when all is over.
The daycare guy being a love interest on the other hand, I can do without. We already have a jealousy subplot, and Maya doesn't need more reason to be worried about Michiru leaving. Michiru has already flaked once, almost flaked a 2nd time, and Maya has her abandonment trauma from her family as well. Adding another romantic rival to the mix is just putting a hat on a sombrero.
I do enjoy that our female leads still clearly love each other, and aren't really trying to game both sides. This story overall seems to be about them overcoming their pasts and trusting each other to get back together. And when that is being focused on is when the story is at it's best imo.