I see valuable things from both perspectives. From Twitch’s point of view, anything to help prevent people from hitting the API hard is a win for them. On the other hand, returning 200 - OK when there still could have been an error somewhere in the mix is a bit counter-intuitive, and an annoyance to the developer. A compromise that I could see would be to return an 4XX error, and then in the content put all of the malformed/erroneous data you provided. That way you can just filter out everything that was wrong, update your caches, you only need to make one more request as opposed to individual requests, and you were directly notified that there was in fact an error.
But in the end, it’s up to Twitch to decide what they want. I’d just like some form of uniformity across the API, which there is surprisingly little of.