I said it was detrimental. Holy doesn't give you the opportunity to do any aoe management because you immunize mobs to stun really early in the pull. People don't complain because healer's doing dps, good enough they just deal with it. Doesn't make it nice. And this is far from being the only example.
So AoE management is detrimental to AoE management. Ok. Except that by the time you've stunned them, eg. those worms, they'll already be casting their AoE and thus there is no real loss to interrupting it - and while stunned x 2 there is ample time for a tank to do whatever they feel is appropriate for enmity. It is also not likely that a WHM would be casting Holy at any point before the tank is in their desired spot, unless - like me - you occasionally consider a QC/Holy while sprinting vs half of a double pull to give tanks breathing room while they move to the next batch. There is also no need to 'leave' that area until you've done a whole session of PoM/TA/CS + Holy Bonanza seeing as it'll interrupt all of them until the time your buffs have faded, and let's not pretend like there's anything else to do provided you have opened with Aero 3.

You can talk about weaving and pet heals and all that jazz - but at no point in any Burn run as a WHM (of which I've done many) has anyone even considered complaining about me annihilating all those massive pulls with Holy, nor was it detrimental to healing, tanking or DPS, nor was it difficult in any capacity at all. As an ex-PLD main and a War-alt partial to Low-Blowing problematic mobs to stop casts such as Worm AoE (ie. two tanks I loved stunning with), I would be very happy to have myself as a Healer.

I have never ever heard a tank complain about Holy Stunning a mob they wanted to stun, this seems so far fetched it's probably made up.
I can recall two instances where a tank whined about my Holy - once when "The Fractal Continuum (Hard)" was the 'latest' - a PLD complained about my holy spam against a double-pull - he genuinely preferred I didn't do DPS at all simply because the pull contained a Minotaur, so he and his friend kicked me out, which is hilarious given said group had no actual AoE in terms of DPS roles so I was out-performing the damage dealers in those situations and neither the tank, DPS nor myself where under any actual threat of coming even close to dying, nevermind getting damaged. As someone who plays tanks AND healers myself, all I could do was laugh and enjoy an instant queue-pop that gave me a group (with another PLD) who laughed along with me at it, seeing as I entered and jokingly asked "You're not going to kick me for using Holy like the last bunch, are you?" - when I tank, I'd have loved that healer - the most I used to get at the time where AFK'ers who'd Cure 99% healthbars back when that was far more prevalent.

I forget the specifics of the other incident but I definitely remember two instances of tanks taking the time to stop playing and get salty about Holy, without it being a conflict between DRK/WHM who refuse to adapt to eachother (Holy vs DRK's AoE sustain).