This but unironically. You learn over time how to read subtitles without having to focus on the text. If you’ve ever tried speed reading, it’s a similar skill. You’re not really reading each letter of each word, you’re just kind of absorbing the pattern of the text to help inform how you interpret what you’re hearing.

With worse hearing loss you’ll obviously not be able to rely as much on the audio and will have to focus more on reading, but in those cases I don’t think anyone would argue the subtitles aren’t improving your experience of the video.

If words flash in front of my face, I end up reading them

That's a dumb dismissive response. It's a passive entertainment medium, it's not supposed to require any skill or effort at all. The subtitles being on screen makes the experience significantly less enjoyable for many of us, and that's all that needs to be said for it to be 100% valid