If 50 people work twice as fast the scope will increase beyond 2x to accommodate the resourcing. As well as to meet increased expectations
The other factor to consider is that the nice-to-have wants from greater productivity in labor may just be required for me to accumulate more scarce resources especially as the population of the world grows. Opportunity cost eventually make me prioritize my investment elsewhere rather than adding scope as you say.
The industries where AI doesn't touch/win, or have real world scarcity constraints even in the face of AI is ironically where the power will be. Hence people saying to get into trades, and physical skilled jobs where we are still winning the arms race against AI for some time yet.