A first playthrough is not necessarily blind. A no spoilers playthrough is not necessarily being played for the first time. A fresh playthrough could just as easily be someone who hasn't played the game for several years wanting to do another run from scratch.

I'll play devil's advocate because either people are overestimating the threat of Twitch removing a tag or they are just overcomplicating language to make the situation appear more confusing and grim than it actually is. Almost all these points can be cleared up in conversation with the streamer, whether they should depends on them.

Additionally, theirs's nothing inhibiting the streamer from still using "blind playthrough" in their title, Twitch simply changed the descriptor for their tags but people are seemingly being puerile about it as if Twitch's decision is an egregious violation of their freedom of speech.

They've taken a stance, theirs's no law prohibiting them from still using "blind playthrough". The streamer doesn't have to agree with their position if they don't want to, what's the problem here?

It's completely ignoring the connotations of language and how it has been used over time. The term "blind" isn't from an offensive origin like several other ableist words that have fallen out of usage recently.

Regardless of the phrase being offensive or not, the opportunity cost is the same. The impact is no different than Twitch splitting "IRL" into various categories but streamers still using "Just Chatting" regardless. If we entertain the idea that the phrase is offensive, are you then suggesting that the change is valid in that context? If that's the case, then this really isn't about the inability to use a certain tag.