Disc valve motors are not reed valve motors. End of story there. :-) They wouldn't be "also" There were some motors in the distant past that were "mostly" piston port, and "a little reed valve"
Disk valve motors have less intake restriction, but also only work well at the design rpm. Their intake timing is fixed. That means they make less power overall than a reed valve motor.
Reed valve motors have infinite intake timing. More importantly, they have exactly the right intake timing. For whatever rpm you're running. Yes, thy are a slight restriction. Typically the breadth of powerband you get more than compensates for the slight loss of top end. And the looses are remarkably slight.