That's a simpleton viewpoint.
Gregory does not cost the team money (cap space) while suspended.
Gregory does not accrue time towards free agency while suspended.
If Gregory's suspension is lifted he has value to the team.
Irving doesn't cost the team anything either because he isn't on the roster, and if Irving were to recommit and finally become active then he too would have value. Whether or not Gregory is further away from free agency is kind of irrelevant if he never plays.
The only real difference between the two is the fact that people have accepted that one of them is a lost cause while still holding out hope for the other.
The day Gregory's suspension is lifted is when there will be a meaningful difference between the two. Until then, they offer the team just as much as you or I.