Ah, but there's a lot of politics and personal-influence-opportunity in management, that's the barrier.
> But you know who will reliably earn more than the data scientist in three years? The data scientist's boss.
I'm not 100% sure of this. There will be a boss in the chain that earns more, but actually I suspect that this isn't always true, given one assumption - the boss, as a job requirement, has to have a good knowledge of DS (maybe an ex/senior DS?), in which case this barrier ensures management will get higher pay - otherwise they'd just stay/go into in DS.
Yes, there may be micro-fluctuations where every company is suddenly scrambling to hire the latest flavor of the month (e.g. data analyst is now data scientist). These are hard to predict. But you know who will reliably earn more than the data scientist in three years? The data scientist's boss.