The whole overpowered thing is really based on what the market wants.
The fact is that most people that can buy a $500K+ boat work really hard and have less free time than they'd like. The bigger engines are a result of meeting the demand for speed from potential buyers of these new boats.
If we look, the market for full displacement boats has really morphed into a market for retired people that want to explore the world. Thats why the krogens, and nordhavns are doing so well. These are expedition boats, vs the boats purchased by still working people are recreational boats.