@chatnoirchatgris Certainly switching halfway through would have been jarring, so that doesn't give you much freedom on how to handle it.
But on the basic question . . . yes, it's extremely uncommon. The Hulk does it, but that's about it. Purplelibraryguy would never refer to himself in the third person; Purplelibraryguy employs normal diction.
But consider the senpai/senior debate. Some people like sticking to Japanese, some people prefer translating it to English. But I don't think there's
anyone who says "Just remove them saying it at all because nobody calls each other 'senior' in English and it sounds weird" even though that would be quite true. Rather, it's generally agreed that Japanese people calling each other that, has to be dealt with somehow--it's a fact of what they're saying and you can't just leave it out. It seems to me that excising the first-name-instead-of-I is like that--it's not so much a translation or not translation, it's literally leaving a piece out. And, it's doing so because the readers are presumed not to want to deal with Japanese people acting Japanese, when that is precisely what the readers have decided to read about.