There is obviously no doubt about it that stable coins are incomparable to bitcoin as they are not even cryptocurrency in the first place. So in a way, it is more like just trying to compare fiat and bitcoin as you have said or centralization and decentralization respectively. Left for me, I feel there is really no point having them in the first place, and somehow would be more detrimental in the long run but it is what it is.
The only advantage I see with them now is just the ability to hedge crypto funds, and is it not even a lot better and more relieving to do that with real fiat? Till now, I still try to want to wrap my head around their usefulness since exchanges could just list fiats instead with regulation.