I agree for the most part but for the summoners, and I say this as a summoner at heart myself, I do not think we should have our Avatars out indefinitely. Mainly because it would remove the awsomeness of them and they would require to be smaller so not to be always in the way. If you played FF titles before, summoners usually just summon the avatar, they do their attack and they go away until you summon again.

In FFXIV, it should be the same, like FFXI did a bit. BUT I think summoners could summon elemental spirits the way you mentionned, without syphoning mp so you could keep it all the time. So you'd have a pet elemental with summonable avatars for bigger, more special and more awsome attacks.

If not, then you'll see avatars out everywhere all the time (having carby out forever in FFXI isn't the same since he was small), they would probably need to be less detailed and smaller so you don't make everyone lag.