yeah...nerf the ult... instantly making the game a 4v5 by ulting the support or someone that needs to kite? high damage output with 2 shields and a slow? hard counter to most champs? free sunfires cape but does more damage and can punish anyone who's not ranged? no resource bar? yeah, that's not fun to go against. he has no weakness besides heavy cc or a fed adc and he can't easily be out damaged. makes the game less fun and creates conflict like "why did you feed mord" or something along those lines.
my suggestion, get rid of the lower stats while in ult, but buff his stats a bit. I mean, two shields with high dps and taking on someone who is for sure weaker than you to get a free 200 gold? yeah no. either this or change the seven seconds into four. I'm not building zhonyas on a adc just so I can live out mord's ult. or, make it like camille's ult, if mord leaves or is forced out of the circle, it ends. just add some sort of limitation or counter play to his ult. there has never been a ult like this, and there never should be.