Hello everyone!
I wanted to write about a pokemon I’ve found a lot of success and fun using but isn’t on the VR, and I’m here to make a case for why it should at least be an option. I think it’s strong, excels in its niche, and while it has some flaws, is certainly a worthy addition to some teams. This is my request for Arboliva to be added to the Gen 9 PU Viability Ranking.

UR -> C+
Let's start with the positives: Arboliva is tied for the highest special attack out of any legal Grass type pokemon with the two Exeggutor forms. It reaches insane damage thresholds, such as OHKOing Florges with Grassy Terrain Leaf Storm and 2HKOing Wo-Chien with Alluring Voice when ran with Choice Specs. Very few pokemon survive two neutral hits, and most die to one super effective hit unless they’re absurdly bulky.
Arboliva has… weird coverage. On one hand, the only moves it really has are Leaf Storm, Alluring Voice, Earth Power, Hyper Voice and Tera Fire Tera Blast. There's others like more consistent Grass stab and maybe Pollen Puff, but in general you're using Leaf Storm/Alluring Voice/Earth Power and then Tera Blast if Tera Fire and Hyper Voice if any other Tera type. The upside? They're all you really need. Super Effective moves basically guarantee OHKOs, and most top tier pokemon are weak to at least one of those types.
In addition, it's notably bulky on the special side and not really lacking on the physical side, allowing it to be a decent switch into stray Knock Offs and Fake Outs, which additionally activate Seed Sower.
Seed Sower allows you to take a few stray hits even better giving it some slight recovery and honest to God a Leaf Storm that can muscle through most neutral targets if they’re not prepared. It can OHKO Meteor form Minior, for example. You could also run Harest as a potential Sun team, but I don’t feel it’s worth it. Wo-Chien is such a good wall that even with potential Sub+Seed Aguav Harvest shenanigans, it’s not really going to be worth it imo.
As previously mentioned, Arboliva has great matchups into particularly strong pokemon like Gastrodon, Rhydon, Tatsugiri, Toxtricity, Decidueye, Scrafty, and more. And that’s not mentioning the potential OHKO potential from predicted switches from Arcanine, Tauros, Delphox, Passimian, Zoroark, Colossal, Mudsdale, Skuntank, and more.
Also, they have really big numbers in damage calcs. Come on, admit you get a hint of joy by seeing Arboliva doing nearly 400% of Gastrodon’s health.
All of this makes Arboliva a genuinely great wallbreaker, at least in my eyes.
Unfortunately, Arboliva isn’t all sunshine and rainbows. I said Arboliva has a “winning matchup” against most of those pokemon, but the truth is that it’s not as good as it seems. Sure, all of those are OHKOs without any potential survival ranges, but Arboliva is slow. VERY slow. Every single one of those pokemon are going to be hitting you first, and they’re going to be doing a lot. All of those pokemon have moves that hurt Arboliva real bad in return, doing anywhere from 40-60% from a neutral hit. While 60% in exchange for an OHKO is still a winning matchup, it isn’t nearly as good as you would ideally like. As well, while you get OHKOs on switch-ins, you also end up getting forced out a lot from things like Leaf Storm special drops, locking in to a bad move for the current pokemon if you predicted wrong, or simply a revenge-switch, Arboliva needs to switch out a ton. It would really like support, too. Ideally, something with Wish or Healing Wish to keep it healthy enough to keep taking hits.
Even worse is the choice of STAB. I’ve mentioned Leaf Storm a lot because it meshes well with Choice Specs and is insanely strong, but of course is only 90% accurate. You could switch to the more reliable Energy Ball, but you lose a ton of good damage ranges and essentially can’t “muscle through” with neutral hits anymore, especially outside of Grassy Terrain.
These are real, genuine flaws that I feel hurt Arboliva’s viability, but I think they’re far from a dealbreaker. I still think, in spite of the problems, Arboliva is genuinely underrated and has a lot of potential.
Finally, I want to talk about other grass types currently on the VR and how Arboliva compares to them.

Venusaur: Venusaur's main niche is being a Chlorophyll Sun sweeper, whereas Arboliva moreso specializes in being a bulky wallbreaker.

Thwackey, Virizion: Both of these Grass types are moreso physical attackers, with Virizion running Swords Dance and Thwackey running Choice Band. They are both fast and frail sweepers, not wallbreaks like Arboliva.

Rotom-Mow, Electrode-Hisui: Two fast grass/electric types known for great pivoting. Rotom-Mow often runs scarf and Electrode-Hisui is the fastest pokemon in the tier. Neither of which have the same role as Arboliva.

Whimsicott: Very obviously fills a different role, with Whimsicott being a Pranker support pokemon

Wo-Chien: Wo-Chien is a wall, while Arboliva is a wallbreaker. Very different roles.

Decidueye-Hisui, Decidueye: Decidueye is strong for its hazard removal and priority, as well as a great secondary type. Deciueye-Hisui is a pivot which prefers moves like U-Turn and prefers to run Choice Scarf, also being a physical attacker. Neither of them are particularly similar to Arboliva.

Sceptile: Sceptile is fast and loves being used on Terrain+Unburden teams. While Seed Sower isn’t as reliable as other forms of setting up Grassy Terrain, it’s still more likely to use Arboliva WITH Sceptile as opposed to choosing one over the other. While Arboliva mostly wants to support itself, it can totally work to help other Terrain users as well.

Shaymin: Definitely the pokemon who you’re most going to have to debate against using over Arboliva. Scarf sets allow it to be incredibly annoying, while also having a strong Grass stab, Earth Power, and Fairy coverage with the added option of Air Slash for Flying coverage. Also, since it can attack first, it can do much more damage without taking damage. What Arboliva has over it, though, I feel is valuable. It’s much better at tanking hits if something DOES outspeed it (which isn’t terribly unlikely, especially for only having 328 as a scarf user), and Arboliva is much better at punishing predicted switches due to being WAY stronger. For example, switching in an Arcanine on Shaymin could lead to it doing 55-65% with Earth Power, whereas Arboliva will OHKO as long as you’re running Specs.
In Conclusion: I don’t think Arboliva is a meta-defining threat, but I do think it deserves a place on the Viability Rankings at the very least. Its strengths are genuinely amazing, but its weaknesses are also very jarring. I would love to see more people giving it a try and seeing if they fall in love with it as much as I have.
I also have some replays of Arboliva doing well and a small pokepaste of my favorite sets. I’m sure a genuinely talented player/builder could do much more than this, but this is what I got.
https://replay.pokemonshowdown.com/gen9pu-2243876520
https://replay.pokemonshowdown.com/gen9pu-2243862575-qnx11i7uk4pfnqiem44xrn1ndpypjpgpw?p2
https://replay.pokemonshowdown.com/gen9pu-2245392285-m6lm9lmvtl7zrgsvuj37raa06vn4uk8pw
https://replay.pokemonshowdown.com/gen9pu-2245091998
https://pokepast.es/2d2d5c3943421efb
also credits to Theycallmephil for helping me with research!