That's a really charitable interpretation of humans. Humans mine for gems to take everything for themselves; they almost certainly wouldn't share with a wild Pokémon. >.>
Well Pokemon does seem more of a Utopian world where most things get along. I have no problem seeing miners tossing a few smaller/faulty gems to a Sableye who pointed to them good spots to dig. Also with the Ability Prankster, if Sableye feels its been ripped off, it can just snatch a few gems and run off.
This argument is more reasonable than the other one you made for this, I'd say. Some of the Pokédex entries say that Salazzle controls the minds of the male Salandit...but then you don't need to encourage your subordinates if you can control their minds, now that I think about it.
Though I also Shield's dex entry says that Salazzle have competitions between each other who has the most Salandit. With both Salazzle giving off a pheromone I'd imagine to draw in more Salandit on their side the Salazzle would have to give some additional encouragement. Besides, just look at Salazzle's expression:
Even though she doesn't need to do anything else cause mind control (that said the dex entries don't really say it's mind control, it's more enchanting the Salandit), she's totally the type that would toy and flirt (and apparently give a pimp smack to any Salandit that fail her; not quite the "helping hand" we all had in mind).
Alakazam can outsmart a supercomputer/has an IQ of 5000, but doesn't learn Helping Hand. One interesting thing about one of the Gen 1 entries (which appears to have been retconned) was that Ninetales's tails were originally "noble saints", which I think would be fitting; since it was later changed to wizards, I think that it undermines this line of argumentation.
But does Alakazam understand human speech? It's not just the words it needs to know but the emotions behind the words, sentence structure, language concepts, etc.. Alakazam can probably figure out the math needed to launch a space shuttle to the moon, but does it understand the themes of a William Shakespeare's play? Ninetales may not understand 2 + 2 is 4, but it can likely keep up with the bard's plays. And with that Ninetale's skills are more sociable thus more likely to be able to provide a helping hand than Alakazam which can give you answers but probably not nor cares to explain how it got it.
I did also notice the "noble saints" dex entry and how later was changed to "wizards"... for it to then be made saints again in Let's Go. However all that is folklore which I don't try to take into account especially when they're "out there" folklore like that.
That's not indicative of a beam, if you ask me. And if snow absorbs sunlight...it melts. Further, Solar Beam takes 3 turns in hail...and the HO for Alolan Ninetales is literally Snow Warning, which sets Hail. I more have issue with them learning Solar Beam but not HH, though...especially if the logic behind it is, "well, Kanto Ninetales learns it" (which is not what you said, of course; someone else I brought this up with had said it).
Didn't say it absorbed it, I said it reflected the light. And it is indicative of a beam if said beam is made of light which Solar Beam is:
In this two-turn attack, the user gathers light, then blasts a bundled beam on the next turn.
And just because the mechanics of the move doesn't make it effective for Alolan Ninetales to use doesn't override the reasoning. A lot of Pokemon get moves they probably wouldn't use if only because it makes sense in context.
The Ultra Sun entry suggests that they'll help others...but only to make them go away. The Sword entry is much friendlier. Either way, seems conducive to a HH outlook, though guiding and powering up someone's moves are generally not the same, of course.
I feel like this discussion skipped ahead a few sentences. Anyway, you're certainly right that A-Ninetales does have that justification for why it should be able to get HH. So why doesn't it? Well it's actions are pretty anti-social, it's not helping because it's kind-hearted or there's a mutual benefit (like with the Sableye example I gave above), it's doing so cause it wants to be left alone and best way for that to happen would be to inconvenience itself. But unless it has to it'll keep to itself.
There should be some moves which help one climb down a mountain though, right?
Random thought, though to answer your question we do have Rock Climb.