Opening my big mouth here for sec about Abomasnow and why I think he’s extremely underrated, not just Hail, the big tree-man himself. While his typing isn’t that great, he has the absolute best movepool out of all the weather inducers. To list it off, he has two 100% accurate base 120 STAB attacks in Blizzard & Wood Hammer, STAB priority in Ice Shard, the ever annoying Leech Seed and Giga Drain for recovery with Leech Seed working exceptionally well with Hail and hazards, Earthquake to ward off Fire- and Steel-types, Focus Punch, Focus Blast, the extremely underrated sleep move GrassWhistle, and of course a very usable Hidden Power. And then there’s the Hail itself; passive damage every turn to any Pokémon that’s not Ice-type, arguably the rarest typing in OU, or holds the ability Magic Guard/Overcoat. Snow Warning could very well be considered the brutal of weather abilities as, unlike Sand Storm, it affects all but about 5 Pokémon even remotely common in the OU metagame meaning most team will have all 6 members taking damage from it. Abomasnow’s typing however is a double-edged sword; Grass/Ice provides neutrality to Ice moves and can easily switch in on most Water-types; in fact, Focus Blast, Toxic, or Hypnosis is the worst Politoed can do to Abomasnow making it an open invite to a hailstorm and leaving Abomasnow the only weather inducer in OU that isn’t weak to Politoed’s STAB. But the downside to the Ice-typing is a weakness to Stealth Rock on top of already being a grounded Pokémon leaving him open to all entry hazards. One of his ideal partners, Tentacruel, can easily remove those hazards but it’s still an issue. Despite this, I think that Abomasnow is not only capable, but absolutely should follow the examples of the other weather starters and adopt a more passive set/EV spread. Abomasnow has just good enough defenses to pull it off, and yes, I know that Ice is bad defensively but Abomasnow doesn’t need to be this amazing wall, he needs to be able to take a few hits, Leech Seed to regain health and get out and he can do that quite well.
Leech Seed with Snow Warning, imo, should be Abomasnow’s claim to fame, not to dismiss the rest of his movepool of course. Leech Seed is a phenomenal move with Snow Warning cancelling out any Lefties as well as the threat of Blizzard or HP Fire making sure no Grass-type dares switch in. Each turn that’s 12.5% of a Pokémon’s HP gone and right into Abomasnow’s pocket, healing off any prior damage, namely entry hazards. If they lack Lefties, due to Hail, that’s just less than 1/5th of their HP gone each turn and it doesn’t even matter if Abomasnow stays in or not. Add Hazards to the equation, just Stealth Rock, and without Leftovers it will cost the opponent 31% to switch in their Genesect on Abomasnow and that’s just switching into it; add one turn of Protect and that’s 49.5% total damage while Genesect could do absolutely nothing and all the while, Abomasnow heals off its own damage.
Getting away from Abomasnow for the moment, I think that is truly where Hail’s strength lies: passive damage. I think that instead letting the Hail do all the work, add some Leech Seed to the mix and not just from Abomasnow, if you can’t afford to run Toxic Spikes, throw a few Will-O-Wisps around as it's just as tough to block as Leech Seed, get hazards up, just pile an exceptional amount of punishment with no need for prediction on the opponent for switching and of course run Lefties on anything that can afford it to avoid your non-ice-types from being hindered to heavily. I think if a solid hail team is built around that concept, it will flourish.