[demetrius]

> Having a one-to-one romanization for each Hiragana phonetic is far more logical for learners

It depends on the learner’s (and textbook author’s) goals. Sometimes, having a phonetic transcription of the more common pronunciation is a more important consideration.

Historically, Hepburn’s transcription pre-dates Japanese orthographic reform. He was writing “kyō” back when it was spelled けふ. Having one-to-one correspondence to kana was not a goal.

So writing sensē is kinda on-brand (even if Hepburn didn’t write like this, because in his times it still wasn’t pronounced with long e).

[tdeck]

I think most learners probably only pick up maybe 50 words before switching from romaji to kana anyway, so in the grand scheme of things the romanization's correspondence to the kana orthography isn't that important.