I did not express an opinion on what is or is not better here. I merely answered your question.
What Twitch is doing here is the same as they did with the view_count parameter they have stopped updating it but left it in API responses. So they are being consistent here with what they have done before.
OBS was liekly a poor example here and just used as an example of “known software that uses the Twitch API”
An error/warning that might cause the program to crash or cease function leading to a confusing error presented to the user if even an error is presented at all.
Not all programmers will have setup their software to be graceful or even sanity checking incoming data.