I think there is a confusion here. I'm not disagreeing with the R becoming an L. The Ramune example is one you presented that is true.
I am bringing up the L becoming an R. Did you grow up with both languages because I don't know if this is causing the confusion. To most American's when a Japanese person with English as a second language pronounces something with a L, it will generally sound like an R. It is because of the different way we learned to use our mouths and tongue when speaking. Second language problems like this are a global phenonoma. I would probably sound silly to native Spanish people for not pronouncing things right. Japanese tv has foreigners that mispronounce things.
There is a reason why the romaji of a series like Final Fantasy (ファイナルファンタジ is Fainaru Fantajī
that "ru" does not sound like a "L" to most native English speakers. It sounds exactly as written, like a "ru".
Minfillia is a name for a character in Final Fantasy XIV. ミンフィリア・ウォード Minfiria Wōdo Minfilia Warde
Yeah I grew up speaking both.
I think where I disagree is that in Final Fantasy for example, I clearly hear it as "faina
LU fantashii" when spoken in Japanese. Even when I pronounce it out loud, the tip of my tongue touches the roof of my mouth at the "ル", similar to the L in "lewd".
With the English pronunciation of "ru" or "ri" with an R, this (the tip of tongue thing) doesn't happen. It's hard for Japanese speakers to even make that sound, because I don't think it even exists in Japanese.
This is why it confuses me when people say Japanese can't pronounce Ls and substitute it with Rs, because there isn't a single word I say in Japanese that uses that R sound. It's all closer to an L when spoken, because the tongue touches the roof of the mouth. Try saying "ruse" out loud, then try saying it by touching the tip of your tongue to the top of your mouth at the R, and it will sound more like a weird "lose". That's where I'm coming from, because Japanese speakers will pronounce it closer to "lose" than "ruse".