I share the OP's pain we chose to use cognito for the exact same reason and I've had the exact same pain however the evaluation of itself takes time and the inconvenience OP is suffering with is only a function of having users.
If I were starting my startup again I would, in almost every instance, trade problems if we have some success for reduced decision fatigue at the start.
If I were starting my startup again I would, in almost every instance, trade problems if we have some success for reduced decision fatigue at the start.