I was just debating on his second point that our tank heals are strong. Wasn't talking about Tectus at all. If anything, having to swap targets to another tank hurts us because you have to recast soom earlier (0.5s) and lose any bonus soom healing from EM. Buffs won't affect much either; dungeons are tuned around fewer buffs. So raid/dungeon differences don't elucidate anything at all.
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I think he just meant you can't do any two of those things at once: fistweave, aoe serpent, or st serpent. If you want to switch "modes" there is a ramp-up price