Seekability, bitrate adaptability, and subtitles are all built in to properly crafted video files. Codec support is handled with multiple source elements inside the video element.
> The YouTube player is, at its core, a video tag.
Nobody is disputing that.
I'm disputing that "they could just use a video tag" to get the same functionality and I'm sure that anyone body working on a video player at any streaming service could instantly give you a list why it's not something that's only there for evil tracking or business reasons.
The YouTube player is, at its core, a video tag.