Lot to unpack there…
First, CoE rotation is 4 secs, and most classes get 4 elements, so the cycle is 16 secs.
Second, if you can run a GR and only take a hit once every 20 secs, you are not pushing, and then the whole argument is irrelevant. For T16 and 5 minute GR 100s, it is fine to do double or triple damage, because you are one-shotting everything anyway. You will not be able to push GR 120-150s without taking occasional damage and then COE or Flavor of time is the better choice.
With CoE:
You do normal damage for 12 secs, then 200% for 4 secs.
Average damage is 50% more if you are in a long elite battle and can tank. For solo, most people run around and gather mobs while off rotation, then hit them hard and tank for the 4 secs, so they do a lot less than 50% more, unless they are playing mid tier GRs, and they are constantly hitting mobs in between their element. For party play they need a healer, which implies that they are taking damage, in which case Squirts is useless.
With Squirts:
You lose the buff any time you take damage, which means you have to have a shield active all the time, or you are super human and can dodge every attack. If you lose the buff every 20 secs, and it takes 10 secs to fully recover, then you average 75% more damage, but it also means that you can no longer tank because when you get hit, you take double damage.
So with CoE, you gather mobs off-rotation, then tank for 4 secs, but with Squirts, you can not tank at all. You have to dodge and hit the mobs when you get a chance.
I think you will waste a lot more time dodging mobs than actually doing damage if you try to push with Squirts. The only class I can see being able to push with this is Wiz. All the rest will only be able to use it for mid tier GRs and T16 where they are one-shotting everything before they can hit you.
What class (other than Wiz), and on what build, can you see people being able to push 15 minute GRs and only getting hit once every 20 secs? Possibly Necro in a 4 man party?
Still, your argument was that this would be mandatory for every build. I do not see that happening at all.