I'm not a huge fan of nerfing characters either, but given the choice I'd prefer a nerfed Monica used than a Monica not used at all. Even writers who have written a good Monica like Ewing and Stern on occasion have written her below her ability at times. Characters with superspeed in general get nerfed a lot of the time. They're logistically difficult to write otherwise.
ANd most of the time Thor and Hulks power upgrades get scaled back too. Hulk at world breaking levels pretty much was just for World War Hulk. Next time we saw Bruce, he was getting owned by Red Hulk left and right. Thors upgrades likewise were usually temporary. If anything he's been majorly depowered in recent years. I'm sure Thor fans are waiting for him to at least get a half descent hammer to get back to classic status quo levels.
Point being regularly used characters who become over powered usually lose that power upgrade. It's usually something for a specific story.