Treantmonk has been doing some very simple class optimization, breaking each down into a species-less basic build with no subclass and then a basic build with a subclass and comparing all the classes for single-target damage per round. He is not making only damage-dealing options, just realistic options. Which sometimes means choosing a defensive feat, even though he's not tracking defense, because realistically that's what he'd do if he were actually making a character sometimes. For instance he's not choosing Savage Attacker as his origin feat, even though it increases damage a bit, because it's not generally a good choice. He's done Monk, Rogue, Fighter, Barbarian, Paladin, and now Ranger (and will get to the others with Warlock next).
Somewhat surprisingly he had found up until this point that all of them do roughly similar damage to each other. Barbarian was best in tier's 1 (levels 1-4) and 2 (levels 5-9), fighter was best in tiers 3 (levels 10-14) and 4 (levels 15-20), but overall they're all pretty competitive with each other and perfectly viable and all tracked relatively close to each other, which Treantmonk took as a good sign.
Until he got to the ranger. Which, so far with his simple builds, isn't holding up great beyond tier 1 and really doesn't work past tier 2. Not when he builds it focused on two-weapon fighting. Not when he changes the build to focus instead on ranged fighting. Not with adding a subclass. None of his simple tweaks are holding up, and yes this includes using spells to add to damage just like he did with the Paladin, though in a relatively simplistic way with Hail of Thorns.
Of course none of that is conclusive. Others will build a better version I am sure, and he's not trying to perfectly optimize everything. And maybe he made a mistake, or made a bad comparison, or made mistakes in some other builds he is comparing to. And maybe Ranger does better as a multi-target attacker and not a single-target attacker.
But I'd say it's not a good sign for the new ranger, so far.
The core issue is that treeantmonk assumes four combats and one short rest between long rest.
The Ranger since first edition has always been built off of two tropes in combat
1) Sustain Damage
2) Switch Hitting (Good at both range and melee)
When Your assumptions are based on having only a few short combats with no disruption in your combat ability every turn then the ranger is going to look bad.
The ranger was always built on having good but not the best damage every turn with little to no disruption of this.
Evidence of this is in fourth edition where the ranger was the best striker because it had these strongest at will attack in the game in Twin Strike. Other classes can burn powers and spells to do more damage but the twin striker will always eventually catch up.
In 2024, barbarian paladin, and every gish are built off of burst damage. Help them fight and campaigns with few encounters per long rest. Fighter and Ranger are both sustain damage switch hitters so they suffer in those kind of campaigns. The main difference is that fighters have some classes that can tilt them to burst damage if needed.
Ranger does not have a burst damage subclass anymore now that gloomstalker has been changed.