SEF is very useful in HFC, especially on the late bosses(Xhul being a prime example, but it also has its uses on the others, and certain earlier bosses)
And on the topic of new-SEF, I really don't like the idea of it being Bladeflurry 2.0 that relies on Blizzard "AI" and not being able to control where they go. Just fixing the issues with it like lack of Floating Butterfly(and moving targets in general) and lack of buff inheriting(TeB, TP and RSK) would be more than enough, and tuning it in a way where we're strong on cleave but also do decent/good singletarget DPS. If they don't want to tune us properly, I'd agree with Xiaojin and rather just have SEF removed than only being useful on very few fights(2-3 target sustained-ish cleave).
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The thing is, based on how other "AI"s Blizzard uses in WoW work, it WILL be extremely dumb and not attack what you want it to(how could it if we don't get to specifically pick the targets? It can't read our minds, and just going for the closest targets or even "whatever has the most health" won't do the trick). Sure, they might blow our minds with some crazy new AI, but I really doubt that'll happen based on previous experiences with "AI"s in WoW.