The slow decline of FFXIV, a summary.

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B: that the WAR's current source of fun (being an unkillable selfhealing machine) was not originally a part of WAR's fun profile in previous expansions

Slight correction here: the defensives of WAR were always defined by their self healing capabilities fueled by their damage output, even back in 2.0. Their tank stance worked different in a way that facilitated self healing as opposed to direct mitigation, sometimes more, sometimes less - but generally it was taking more damage, and then also healing that up by themselves. But doing damage and healing itself through said damage was the core of the WAR gameplay in ARR and HW. Taking damage and healing back up was very much part of the fun of playing warrior well, it was just much harder to get there compared to today.

That identity had been previously weakened a few times (like with the removal of bloodbath, or when all tank stances became the same skill), and as we all know, CS3 are prone to overcorrecting issues they notice, which is why we are where we are now.
IMHO, the self healing/mitigation capabilities of the tanks, while strong, are not the big core of the issue - its that tanks can heal their teammates with enough potency that it is sufficient to negate the lax incoming damage in most instances, which begs the question "why, Square?" (Bloodwhetting/Nascent is a special case cause it procs per target hit with no upper cap, effectively making it a braindead bene every 25s in an AoE scenario - that does need to be adjusted).
Tanks should not be able to heal others as well as they can at the moment. Thats a healers job.