1. Lateral progression. In ffxiv you get a piece of gear that you use for one job, and the next time the game is updated that gear is deprecated and replaced by the same item with the very same stats just in slightly larger numbers. In FFXI there are some pieces of gear that have been in the game since its inception that are still sought after and used to this day.
2. Swapping gear on the fly in combat. This adds a new level of depth and strategy to how you gear your job. Rather than having one catchall set that you're locked into, you can collect a variety of gear to suit many situations and swap to it on the fly.
3. The best transmog system in any MMO. It works like this, if you own a piece of gear and you can equip it on one of the jobs that can use it, you can transmog anything to that look. No fuss.
4. Better storylines. FFXI has compelling storylines which make the world feel lived in, and make you feel like a part of something bigger than one person, rather than a walking deus ex machina.
5. More jobs, and you can use a sub job. In addition, the classes have greater variety than in ffxiv, each have a distinct playstyle and fill specific roles rather than having different flavors of hotbar and gcd based combat.
6. Trusts. To the uninitiated, trusts have been around in FFXI for years. The system in FFXIV will no doubt be neutered and tame by comparison.
7. The game isnt overrun by degenerate ERPers. Self explanatory.
8. Monthly content updates
9. Better music
10. There is a level of depth to everything in the game that FFXIV will never be able to achieve. There are too many nuances to every aspect of the game to outline in a single post. FFXI is like a vast ocean, large and deep and full of possibility. FFXIV is like a reflecting pool, pretty but shallow and boring.
Bonus:
Mithra will always be superior to Miqo'te