No really, once you hit 90th, there's a lot more to SMN.

Sure you can summon instantly... but the rest of the powers underneath those aren't so fast anymore. Specifically Garuda and Ifrit. Ifrit powers were already long cast, Garuda the powers cast fast, but are dependent upon laying down your AoE DoT field first, with the DoT running underneath them, otherwise they're not that strong. And the DoT has a long cast time. Titan isn't so bad those are still insta-cast, but the others... well not so much. Bahamut and Phoenix still are mobile, but those are only in between all the others... which you have to use in the mean time.

I didn't realize just how much they cut down the mobility of the SMN until I played that Barbaricia one... I couldn't get off damn near anything, other than the base summons for Ifrit and could not lay down my DoT for Garuda except once or twice, otherwise I was running for my life around the battlefield only able to get off a Fester or two.

RDM, Was only a very short cast time for the first one, then sliding dual cast for the second.

Again this is not the summoner of old guys...