Theoretically, they aren't putting Morde bot because he's a strong carry, but because he's strong against carries. Ryze, Cass, and Azir bot all work perfectly well and are basically AP marksmen, but Morde isn't supposed to be a replacement for a marksman. Morde is supposed to be the champion that doesn't give a rip about being stuck in a duo lane or being stuck in a ranged dominant lane because of his strong pushing and self sustain and anti-poke shield. Basically, Morde is designed to be an ADCs worst nightmare, assuming he has someone with CC who's able to lock his target down for him.
In theory, it's a stroke of genius!
Practically, they gutted everything about him that would make him ideal for the task at hand, leaving him undoubtedly outclassed and 100% useless. nobody cares if you outlevel the enemy if you can't actually all in at 6 because you get kited to death. Nobody cares if you have a potent max shield strength if you can't get it to stack in the first place. nobody cares if you can eat poke if all you're doing is being a bit annoying and forcing your DPS into a solo lane.
If they wanted morde to be a duo later, that's absolutely fine, just they actually have to know wtf they're doing when they try to make him adjust to it.