For the sake of the scenario, I'm going to label the number 1 skill as the "filler damage", and number 2-5 as "situational spells".
The way I envision playing the class efficiently, as there's a minor cooldown on the ol' switcheroo, an Elementalist would only switch attunement to use specific situational spells, using filler damage according to the current attunement in order to be prepared to use another situational spell at will. I'll draw out a scenario to show what I mean.
We're playing the Battle for Kyhlo, and are assaulting the enemy-held clocktower, specifically the elementalist (me in this made-up case, wielding a staff) and two of my chimpanions. I start out in Air attunement for the speed boost up the stairs, and when we reach the top we've got two hostile defenders to handle. I start tossing out filler lightning at them, and suddenly two rangers appear in the windows. Immediately I attune to Earth for the projectile protection and toss pebbles at them. My companions notice the rangers and manage to close the distance (with, for example, an Engineer's Backdraft). As they're starting to take a pounding by now, my attunement of choice becomes Water to throw out some minor healing to them (with a few water bolts for filler), and then Fire for some lovely AoE on the clumped up enemies (filling with Fireballs). After a miraculous victory and cap I'd switch to Air again for the speed boost as we speed towards our next objective.
I hope my thinking gets across. My understanding of the attunements is that any of the filler damage abilities are just as good as the others (roughly), with the main difference and hence your reason to switch being your situational spells. Rather than switching to whichever filler damage ability that does more damage whenever it's off cooldown, I see the most efficient way to play to be keeping as many attunements off cooldown for as much time as possible, to be able to adapt to ever-changing situations.