I would say utility is any non-damage contribution that helps the group. Healing, rezzing, interrupts, mitigation, etc. Most damage buffs are included in rdps, saying they count as utility is just a different (and less clear) way of comparing rdps vs adps.
As for which jobs should be higher or lower, I'd look at it this way:
1. If two jobs have exactly the same potential output but one offers something the other doesn't, why would you play the job that offers nothing? Downplay it all you want an advantage is an advantage, even in a seasoned group people can screw up, having an extra rez is nice. Clearing a little faster is also nice, neither is that big of a deal for a good group, it's more a matter of preference.
How much having a rez should cost I can't say but it should cost something. Balance is most important for prog, afterwards when people have experience and better gear it doesn't matter as much who has a rez and who doesn't, nor does it matter as much who deals more damage, you're getting the clear regardless.
2. Same goes for ease of play. If two jobs have the same potential output but one can be executed with a single macro while running around as much as you like while the other requires the group working around you to make sure you're able to keep dpsing, fun factor aside there's no reason to play the difficult job and those who do because they enjoy it will likely end up discouraged.
Imo jobs should not be balanced around max potential for this reason, nor should they be balanced around the worst players as that will create too large of a disparity at the top. Finding that magic number where the most people are satisfied is the hard part.
3. Jobs that buff the group can only ever be as good as the whole group. Their max potential rdps is higher by nature but their lows are also lower, the more buff-centric the job the more their own rdps is out of their control.
SMNs offer a good amount of utility: Free healing for the group + a targeted heal every 2 minutes that doesn't come at the cost of dps, a decent self shield every 30s, and the ability to rez which only one other dps can do. They are extremely mobile and ranged with an incredibly straight-forward rotation that's almost impossible to mess up - it doesn't always do well with downtime but that's a design problem more than a numbers problem. And they have a raid buff. It makes sense to me that their adps would be among the lowest.
Their rdps is dependent on the group making good use of their buff which thanks to its long duration is not difficult to do resulting in less variance compared to Ninja for example which would result in SMN's max potential rdps being lower while their low end should be higher.