People are really calling alts being extra inventory an exploit? I have to laugh.

Maybe if the game had a better inventory/storage system and if they actually made a real glamour log then this wouldn't be such an issue for most people. The game is also littered with too many currency-like items that just clutter your inventory. Regarding the Armory Chest, at some point it won't be able to hold every weapon/tool for each job when they add more jobs into the game.

Alts are a cheap but pretty time-consuming option to the current mess the inventory system is. Transferring stuff between your own characters via FC chest is an exploit? If it was, then the devs would've done something to make it so the game detects and prevents transferring items from a character you own into a different character you own. Someone here will probably blame it on spaghetti code, though.

Mailing between alts is already possible. The system already allows it since it treats two different characters from the same account as two different people entirely. The only exploit here is being able to friend your alts through working against how the servers work.

I really don't get why you can't add your own alts as friends anyway. To prevent RMT activity? Might as well delete the trading system entirely. Trading via by mail is essentially the same thing, but more tedious.