Honestly, I was there when 4.3 dropped and I did feel that Tsukuyomi was pretty much pushing the limits for what a mandatory MSQ fight ought demand.

I feel the main issues are the min iLvl (which was probably demanded by the xpac roadmap, but is really too low for the average DF group to be comfortable; when helping people through it in 4.3 I found it went much smoother using PF and requiring 350) and the fact that there are certain mechanics combos here that are really punishing, and even beyond what Extreme demands (the most notable being that Normal - and only Normal - combines the half arena AoE with Shiva circles, and you often must wait for the Blade AoE to go off before the safe spot for circles is available; the dodge time for this can be extremely tight, and any mistakes result in a party that is very vulnerable to wiping to Lunacy).

(As an additional emphasis-aside, let's keep in mind that Shiva circles alone are considered an annoying enough mechanic that the popular PUG strats for fights featuring them - including TWO of the current ShB Extremes! - routinely simply eat one and deal with the vuln as the path of least resistance. Here you can't even afford to do that, and this for a STORY mode fight at that ...)

It's undeniably "that one boss" of SB, even more so than Shinryu.