Solar Beam Ho-Oh, Blizzard Kyogre, etc.

Against Ho-Oh with solar beam, A-Golem's electric sub-typing removes the double weakness to grass, which *might* allow it to avoid getting one-shotted. It also loses the double weakness to water, which could also help it survive hydro pump from Lugia, if that ever makes another return. I'll admit, I haven't powered up/fought with any of my A-Golems, so I can't say for sure how well it would perform.

As for your Rayquaza team, forget Ice Castform and bust out the Delibird team with ice punch! 😁 /s

Alolan Golem is solid, I’d say it’s better than Kanto Golem. It loses its double weaknesses to grass and water and gains double resistance to flying. It can learn Wild Charge, making it a solid electric attacker. Volt Switch kinda sucks for attacking but it’s great for defending. If you want pure rock, it knows rock throw and stone edge/rock blast. It’s obviously nowhere near as good as Tyranitar and will be outclassed further by Rhyperior and Rampardos next gen, but if you have it you might as well use it.

Against flying moves he is better. About Ho-oh I'm not sure cause he will likely die to a SB even without double weakness.
On defense he is better but who even cares with the current gym system?!
I'd say it's a draw but I wouldnt put dust in any of them. Which means the normal one is better cuz you can catch him at a high level.

Just gonna drop this here. It goes into what you need to know regarding the more interesting Alolans.
https://pokemongo.gamepress.gg/alolan-pokemon-what-you-should-know