I like your optimism towards the new Ho-Oh~
I was thinking about trying it out in Volcanion, but it seems like a "win-more" card.
The reason I say this, is because:
Volcanion already doesn't have trouble OHKOing.
130 + Choice Band + Steam-Up = 190
Which, as you stated, will kill most basics.
What's important to think about, is what it means for Ho-Ohs attack to cost 1 more energy.
This is an additional attachment or energy to accelerate.
That's one turn behind, and/or one less steam-up.
With that one energy, you could swing for 220, instead of 190... which... I think kills anything that's relevant in the meta, except Lapras + FFB, but that's just one additional steam up on a card that's already kind of slow setting up.
Especially since Decidueye and Solgaleo are already weak to fire.
and there's almost no situation in which I would want to use Ho-Oh's GX attack over Turtonator's.
Especially since:
1. Pokemon Stretcher is a thing.
2. Oricorio does the same thing, but it's from the deck, isn't limited to EXs and GXs, and doesn't use your once per game GX attack.
There's already a lot of cards competing to get into the Volcanion deck (ex. Starmie), and I just don't see this card offering enough to warrant a spot.
I agree with your assessment mostly, I just think the extra 50 damage is worth the energy attachment.
Back story: I play Volcanion. I sometimes have problems late game if I have had a couple Volcanion's Prized/KOed and/or I can't find Choice Band, Energy, Energy Retrievals, etc. I started playing 2 Turtonator GX partly because of the GX move, but partly because I need one less Steam Up/Choice Band to hit the same number as Volcanion.
When I look at Ho-Oh, I see a sustainable Turtonator GX that costs one extra energy, hits for 20 more damage, and isn't revenge KOed by Volcanion, Lapras, or Ninetails.
Is Ho-oh worth a spot in Volcanion? Maybe, but I'll probably only play 1.
Also, I like Ho-oh, so I'm a little biased.