it’s absolutely not the same as modding every game. Gameplay remains original, and a thingy that optionally goes “ding, you did a thing!” every once in a while is so far from the biggest ruiner of experiencing games “properly.”

Not all mods drastically change gameplay. Adding goals that never were in the game can totally influence how you approach a game. Doom was definitely not designed for secret hunting but when I first played I stayed at each level trying to find all the secrets because my map showed me how many secrets are left (a feature of Crispy Doom). Would I spend all this time hunting for secrets if there was no secret count? No, of course not. I wouldn't even think about it.

How about pretty standard features like save states, rewind, and so on?

Save states can definitely be abused to ruin a game for you. E.g. if you save at the start of every level of Super Mario Bros. If an emulator did this automatically, would you recommend it to new players who want to learn how SMB felt back in the day?

it’s a weird choice for a developer building a tool, who presumably cares about community feedback, to say no to an overwhelmingly popular feature.

I'm not familiar with what actually prompted that Cohost post that Kayin reacted to but it sounds more like the developers didn't really refuse to implement but more that the project was young and they didn't implement RA support yet. RA support is nice and all but having decent performance and no game-breaking bugs is more important.

It was the unfair strawman arguments that the author brought out to throw shade on achievement developers, to the point where the author had to invent naive or nefarious motivations for doing so. Simply the least charitable, lowest empathy, most intellectually dishonest takes for throwing shade at some volunteers making stuff for other people.

Yep, I can see that. Whoever Kayin argues against is unlikely to be present in the RA developer team - if such a person exists at all!