What I would be proposing is both deleveling + harder to level up + require mandatory EXP parties beyond lvl 10 to level up + impossible to solo beyond lvl 10 + impossible to PL.
I don't understand... Why do you want FFXIV to be exactly like FFXI, if you could just go play FFXI? They're even adding a new expansion for it, I fail to see your loss here. Before you look at my character's levels and note that I've barely gotten one job to 50, I'll also note that I didn't really play FFXI that much, but I did try it. As a casual player, I found it annoying to hit level 10, run over to the dunes, and have to find a party every time I wanted to play for a half hour before class or work.

Most of the time I was unlucky enough to login when there was no dunes parties happening, so I pretty much couldn't do anything. MMOs should have options, and they've progressed to the point that leveling is a means to an end, but not so much the game itself. The leveling process teaches us how to play our characters by slowly giving us new challenges, and introducing us to new skills. De-leveling in FFXI, or everquest, or any game it's been in, is just a time sink, and it's a time sink that can turn many people off of the game.

Being able to solo to level works, because it gives the guy with not much time to play the ability to login anyway just to get a few leves on a job before he rushes off to do whatever. Now, I'm not all for solo content the whole way through, by all means, keep parties mandatory for all progression that counts after hitting level 50, but let players level solo if they so wish.

If you want to do exp parties, do them. Don't take away a current core aspect of the game just because you want the entire community to play like you.