Solteris? You mean raid geared? That's not "appropriate", that's "overgeared". Crystallos difficulty was appropriate to raid tanks when it was prenerf Ashengate/Frostcrypt being appropriate for Demi/DK tanks, not a year and a half later for Solteris tanks. I know all about Solteris level gear, that's what twinks in my guild wear, for the most part. My own warrior twink is about half raid geared (8/20 slots Solteris/SoFtier2, all the rest is group stuff). I DUO Crystallos with that warrior. That's not in any way appropriate! It's outlandish and silly! Appropriate for Crystallos is 500 to 800 ac less than Solteris, and sketchier mods. I've done that, too, and it's ... "exciting"
Survival actually depended on the healers and debuffers using all the tools available to them. When you were trying out CoA/demi (raid stuff still? hmm) tanks yourself, did you ever have the puller kite for a second so you could drop the full debuffs (Gelid Frost, Hand of Ro, Fixation of Ro circa 2008 here) on each mob, and only have the tank engage after casting Reptile? If not, why not? The extra tools aren't there just to turn "easy" into "cakewalk", they're supposed to turn "undoable" into "doable".
And btw, I don't quote devs on data. Devs aren't good sources for numbers. The right thing to do is go past the devs to the players they got the data from, or just plain generate it yourself. AC isn't as easy to check out as slow, but it's entirely doable.