The impression I get is that while SB can mimic someone's powerset, she can't actually mimic their experience at using them.
The impression I get is that she has to choose between "Can produce a lot of clones but have very limited autonomy and functionally zero creativity", or "Can produce one clone and have it very convincingly mimic the personality of who she copied (Which is probably what was done for the Uiara thing--unless it literally was Uiara doing it, but she was under high end mind control at the time--we do know the Philosophers seem to love their fucking telepath bullshit), but she still can't make the clone do something she can't wrap her head around personally, so the higher end Metahumans who deal with exotic bullshit are too risky for her to want to play around with given how bad fucking up can be, and all of them fundamentally lack agency--so they have no ability to volunteer information either. Easy if, say, you want to have one read out a script and genuinely believe in what it's saying. Not so easy to clone someone and then interrogate them for all their secrets. That'd probably cause Resonance if the clones were that perfect, and we know she can clone the powers of people who are still alive. It's not causing Resonance, so therefore it can't be a mental copy.
So like, if she were to copy Black Swan, she'd get the Hit 9 version from the start of the game. Sure, that's a dangerous A-lister, but that's not the "Candidate for strongest Metahuman" which Mona is. Even if she copied Black Swan's powers and personality, she wouldn't be able to just instantly deduce the weirder edge-case stuff like Hypernovae Mode and Lightspeed Dash, and probably wouldn't want to risk trying it and fucking up because that kills everyone in the same area code and presumably she can't actually survive being in the splash zone of a superheavy nuclear fusion reaction.
Ultimately, she's an Ops and Espionage S-lister, with an arbitrary amount of tools in her box, but the more she tries to use at once, the less effective they presumably become, because a lot boils down to Experience being the god stat, and it doesn't matter if you have a toolkit full of Every Tool if you don't have the time or inclination to master any of them.