Ah, sorry, I misunderstood. ^^
That was my experience, at least.
You need vocab and grammar to read, but you also need to read to actually be able to cement and retain vocab and grammar. I think it all needs to be grown in tandem.
I saw that @ccookf already went into it, but the games that I played were indeed Ace Attorney games. They are more “involved” than the average visual novel. Rather than just reading a story while making a few choices that funnel you towards a specific ending, there is more to it. You have to pay attention, know what evidence you have, and catch out mistakes during witness interrogations.
I had played the game before in English, which was my saving grace. If I had known absolutely nothing, I would not have been able to play that as my first Japanese game. Especially since there was no furigana, and I didn’t have anything like a text-hooker.
Knowing the major plot points (I didn’t remember most details, since I hadn’t played it in years) meant that I had enough knowledge to progress the game while understanding about 5-10% of what I read during the first few cases.
It was most certainly a grind, but by the final case, I understood 80-90+% of what I was reading at any given time, since I had kept up with WK and Bunpro throughout those 9 months.