That's pretty much exactly what it is. An attempt to "strengthen" an argument by making an absurd one and trying to use it to support a position it doesn't really support.
As you point out correctly, Tanks are based on Melee design principles, not Caster ones. Healers are based on Caster design, arguably ARR 2.0 SMN (a cure spam nuke, DoT upkeep, and some oGCDs for additional damage and healing, with some token backup GCD cast heals).
I thought it would be interesting if one was based off of something else, like Ranged (either proc based or MCH-based; before 6.0 I pitched Chemist having a caster/magic gun and having a 1-2-3 rotation like MCH with a Mudra-like "Mix" command for its Job Gage/gimmick, and could see SGE working with a 1-2-3 rotation of shooting lasers at things like that, too), but at present, all Healers are designed from Casters.
There was also no one who said "tank players would probably be fine if it was just 1 tank that was like this," the actual quotes were:
"WAR players, for example, just seem happy to be solo 4 man parties. Remove their 1-2-3 -4 and just let them spam Fell Cleave over and over, have full uptime on Bloodwhetting, then Primal Rend once per minute and some Orogeny in there somewhere, and there are quite a few WARs that would be happy as clams over that.
Not saying they all would be, but they probably wouldn't be rioting over it."
"Again, not saying everyone would be thrilled, but quite a few WARs just love being a nearly unkillable god of battle and love the dopamine hits from Feel Cleave and Primal Rend, so "MOAR Fell Cleave! John F---in' MADDEN!!!" would make plenty quite content."
But, just as many would be fine with it, many wouldn't care for it, just like any change to anything will always alienate people that play it. And WAR is arguably already pretty simple. But there is a segment of the playerbase that wouldn't mind being able to run through dungeons with permanent Bloodwhetting, Primal Rending their way down the hallways of dungeons, and fullhealing with each Fell Cleave. I'd think that would get old after a while, but...some people are content with such things forever.
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The changes for Healers are obvious - have encounters actually require healing; make the Healer Jobs play more distinct from one another.
The changes for Tanks are also obvious - have encounters actually require tanking (positioning, threat management, etc); make the Tank Jobs play more distinct from one another.
EDIT:
And, on both counts, that means continuous requirements from the encounters, not once per minute or whatever, solved with an oGCD.