All that proves is they have a reward/incentive problem.
If you cant manage your inventory, thats on you. If someone hasnt organized their inventory since they started and then 70 levels later "find they are bogged down" then thats their own fault. Even crafters shouldnt have a problem with all the storage, unless they are trying to level all DoH and DoL jobs in tandum, then, again, that's a problem of their own making. I only leveled one DoL job and max 2 DoH jobs at one time.
To address the gear, they have added the glamor plates and increased the armory storage and still, manage your crap. At the worst, before Stormblood launched, I had both retainers completely full of gear, cause thats something i do hoard. But I solved my problem by actually going through it all and asking myself "why do i still have this hat/pants/chest? When was the last time i even used it for glamor? Where did i get it? If i decide i really want it again, i can do unsynced runs of X dungeon until it drops." If they have any problem its an item bloat problem. So much useless, pointless, crap that "cloggs" up your slots.