You can´t compare a MMORPG with defined classes to a singleplayer game where you say the characters use X, use Y. Everyone his opinion, for me it doesn´t fit MNK as a melee class in any way, especially with the given tools, which fits the class perfect and give MNK uniqueness in some way.
a) Yes it´s useful, but not needed. In 99,9% of all cases you´re in a group and some with a range attack anyway.
b) You can hold uptime there. Use backdash / SSS to move in your direction, turn around halfway and dash to the boss. The thorns won´t do anything and tethers will break. It works 100% unless the heal / tanks sleeps and stucks mid. I don´t even now if a range attack would be in range since i played it that way every time with MNK / SAM.
c) Another thing of timing. The castbar takes ages, find your timing, use SSS and dash in again.
d) I think i´ve played them all and it´s possible to work around them. Behemoth might be somehow bad with the safespots, but again i would call it "timing". I do even got invites to the solostuff without a buff since i started to do them with MNK and not as a tank or heal.
e) A thing of timing SSS (maybe with dash) again.
So yes, the only content where it´s somehow really useful is PoD and HoH. But again, it´s not really needed normally. You could even use Entlightenment for those, since chakra is easy to gain out of combat. That i´ve used the word "timing" so often is, because that´s exactly one of the biggest point about melees. A well timed SSS is a super strong tool on MNK. Other melees have other decsions to take in such cases.
And tbh... Dungeons, Bodzja, Fates or whatever... it doesn´t really matters what you do there, just survive somehow or wait for a rezz. Since the new Relic is just again pretty much the same pointless grind like the ones before, i play it completely brain afk, even die here and there because Netflix is more exciting.