If someone has watched anime with English subs for thousands of hours before starting to learn Japanese, how much of a head start does that give them?
Remember the "watch 10,000 hours of Eng subbed anime" joke from DJT?
Well, I actually did watch anime with English subs for thousands of hours
before starting to learn Japanese.
I can't talk for everybody of course,
but my experience was that
I knew literally nothing before I sat down and started formally studying the language.
I picked up probably no more than about 50 words total,
When you're watching anime with English subtitles, you're reading the subtitles. You're only partially listening to the audio. So I imagine that the only advantage a person who had an experience similar to mine would have is a little more phonetic awareness. It would be easier to parse the sounds. Phonetic awareness contributes to pronunciation down the line. They would still have to build their understanding of Japanese almost from zero.