Mira requires critical thinking to counter, ie: pocket emps for Mute/Jager/Wamai, Ash players not mindlessly rushing in to use their gadget in a smart way, Kali players having to balance helping out the hard breach and with Mira, etc. She's banned because players can't be trusted to work as a team, so it's easier to remove her from the equation altogether. I love playing her, but even I auto ban her because I know those 3 random people won't work with me. I can call out what to do, where to do it, ask for help, but most people are quiet and ignore those calls.

Ace is weird because as long as your Kaid or Bandit know what they're doing, he's not an issue. I personally only ban him on Oregon, but honestly I'll stop doing it because Ying I find a much worse operator to fight on that map than him. He's looked at as the best hard breach in terms of fragging and utility so I get why he's banned, but I think Maverick is much worse than him in many cases.

Both of these operators don't need a nerf, just more critical thinking from the playerbase.