I couldn't disagree more to be honest. Tangrowth is fantastic in countering Garchomp, Terrakion, and Dragonite. I can't think of any grass type (or Pokemon for that matter) that can claim this. Regenerator also sets it apart from most Grass types, apart from Amoonguss, which is more of a special wall.
Saying Breloom is a top notch wall breaker or that Venusaur is a way better sun sweeper doesn't mean anything. Tangrowth isn't trying to fill these roles. It's like saying Snorlax hits much harder than Blissey therefore it's better.
Dont forget things like Feligatr or DoubleDance-Lando-T, both gaining popularity as they are able to pressure the usual types of Stall, but both usually struggle when facing Tangrowth. The only problem w/ Tangrowth seems to fit it onto a team well enough, as it has kinda an awkward typing for a physical Wall and the Grasstype sadly brings some annoying Weaks.
However I have got another Pokémon to consider:

Mandibuzz @ Leftovers
Trait: Overcoat
EVs: 248 HP / 8 Atk / 252 SDef
Careful Nature
- Brave Bird
- Whirlwind
- Punishment
- Roost
Despite dropping to NU recently, Mandibuzz has a small OU-Niche which sadly just got smaller after the Lando-I Ban. It has an awesome special bulk and solid overall bulk and its typing allows it to deal with things like Alakazam, Latias and Latios, Reun, Trikep, BP-Celebi. It even is an ok-switchin to Venu and Volca. It solves problems Stall usually has, the downsides however are that sometimes it doesnt do anything and it is nearly useless when facing oppenent Stall, so you need really good hazard control (Scarftar + Forry + Jelli worked ok but not perfectly). As a bonus, the ability allows it to be used in Sand Stall without taking Sand Dmg.