Just like Binding of Isaac, they intentionally put a soft-end low on the skill cap. I think it makes a lot of sense to put the bulk of the narrative progression under an early skill threshold; it mirrors the pacing of linear action games better than what we normally see in this structure, and it allows the bulk of the player base to feel like they’ve engaged in the game the high-skill portion of their friends have seen.
It wouldn’t work without the iterated opt-in difficulty mods (and the speed the game encourages you to increase the difficulty is way too gentle since it’s tracked separately for each weapon) but I think they promise harder difficulties to compensate for the explicit permanent upgrades at an adequate time.
Interestingly, people here are burning out before they hit the first end; my sense was that the Darkness buffs were noticeable enough and had clear enough resource goals to propel most players through the first end.
I think it’s better to think of the baseline stat loadout as the completed Darkness set, but I don’t think they did, or, they should have taken back control of enemy damage, health, and speed at higher difficulties because the structure encourages the player to find the easiest high-difficulty setting.