The stages for loot tiers are in the patch notes:
Tech 0 (GS 1-11) – Primitive tools, weapons and armor including a bow and the blunderbuss.
Tech 1 (GS 12) – Iron or similar melee items and armor and and the first proper firearms like a pistol or double barrel shotgun.
Tech 2 (GS 50) – The best melee items, bows and armor and mid range firearms like a pump-action shotgun.
Tech 3 (GS 91) – The most advanced firearms like an M60 or the Sniper Rifle.
I think one of the advantages of the new system is that it disincentivizes cheesing the loot rooms of the larger POIs in the first week since there's no point. You are better off just going through the quest progression and the smaller POIs. If you want to min/max by not opening crates you can but that doesn't sound fun to me. I'd rather open the loot chests and start accumulating ammo, armor, and mods.