Hot take: I think the idea of buffing Hail is way off base.
Hail was at some point arguably the best weather in Gen 8 OU, purely off of the strength of Alolan Ninetales and Arctozolt (and formerly Kyurem). Even now, I don't think it's considered the worst weather in OU currently and it's definitely still at minimum viable-ish.
Sure, Hail currently doesn't really benefit most Ice-types at all, but does Sand really do that either? The strength of Sand teams from Gens 6 - 8 is built entirely off the strength of Tyranitar and Excadrill, both of which are strong even on non-Sand teams. I don't think I've ever seen a team where a Rock-type that doesn't have Sand Stream is meant to benefit from Sand (other than mono-Rock teams). Like, I guess it comes up when your opponent brings a Sand setter and your Terrakion/Nihilego happens to benefit, but that's about it.
Overall, I'm trying to say that Hail
itself is a viable weather, it just doesn't benefit most Ice-types (similar to Sand).
Instead, I'd go a different route and say that under hail, all non-Ice-types suffer a -1 drop in Speed. I'm envisioning this being an actual stat drop as opposed to the passive multiplier Sandstorm's boost is. Not all Ice-types are fast enough for this to be an overpowering mechanic, but it would change the dynamic of a lot of matchups, and encourage players to use new builds and stat spreads (suddenly Timid 252 Speed Walrein is looking like a good idea...)
Giving an outright Speed boost to all Ice-types would be too broken, but a debuff to everything else can be worked around, and would rebalance the existing Pokemon and mechanics around it. So Pokemon with abilities like Clear Body (many of whom already have an advantage over Ice-types) would prevent the effect from being too overpowering, and the White Herb would likely see an increase in viability and usage.
Given how Hail is already viable (with its 2 main abusers at least), think of how absurd it would be for these two. The fact that Hail slows down non-Ice Pokemon makes it much harder to deal with Alolan Ninetales, since you can't Taunt/Knock/threaten a strong hit before it sets up Aurora Veil. With Hail slowing down other Pokemon, you can't use a fast Scarfer (namely Kartana) to revenge kill Arctozolt, and it won't have to choose between a +Atk and +Spe nature anymore. The only Pokemon that can revenge kill it without priority is 252 Speed Hawlucha (and if it does use a +Spe nature, you also need Jolly to be faster, and Jolly Hawlucha is a pretty bad set).
You don't even have to use a Hail team, Alolan Ninetales is now the fastest screens setter (aside from Prankster users)
and it can set both screens in one turn. It's not very prevalent in Gen 8, but in Gen 7 it was a pretty strong enabler of screens HO.
So while this does make it so that Hail actually benefits Ice-types, the degree of benefit that it gives to the abusers that are already strong is
absurd. The proposed counterplay doesn't really work; most Clear Body users aside from Dragapult are pretty slow, and slapping White Herb (or Utility Umbrella) onto random Pokemon to offset the speed drop is a countertech that is mostly useless versus non-Hail teams.
Plus, making the viability of a type strongly tied to a weather condition just seems flawed to me, since only auto-weather is really viable (what is effectively a +1 speed boost for 5 turns doesn't seem that good even for in-game) and that's tied to a small number of Pokemon.
There's more I want to elaborate on (like design trends in Ice-types that contribute to its perception as a generally bad typing) but I'm out of time for now.
