The Economy X product includes more than just the seat at the overwing (or the first 3 rows of Economy on the B738, depending on which seat you've chosen):
Economy X guests travelling on Domestic flights will receive:
Priority Screening (where available)
Priority Boarding (where available)
Greater legroom at the front of the Economy Cabin or in the over wing exits
Preferred overhead locker space
https://www.velocityfrequentflyer.co...ews/economy-x/
So yes, the crew are required to protect the integrity of the product. Regardless of whether people believe it should be sold as a product or not (these economy comfort style products are common practice in the USA for the record), as stated above the reality is it IS sold as a separate product and is treated as such. And if an economy X paying passenger does not meet exit row requirements, they're able to be seated in other non-exit row economy X seats.