If you look at when the "v" form spiked, it's a good bet that Tolkien influenced that a lot. But, yes, it's a common plural form for many (but not all) English words that end in f in the singular. But no one uses chieves as the plural for chief for example.
> It's a mark of the popularity of his books that people assume that's the correct spelling in English
It's more likely a mark of the fact that people are familiar with other common English nouns ending in f, such as wolf(wolves) / leaf(leaves) / hoof(hooves) / elf(elves) / staff(staves). (Granted, some of those are less common than others.)
I see no reason to believe that "dwarf" was the odd noun that resisted that process. Making Middle-Earth language "stand apart from English" by applying a perfectly normal rule of English would be an odd thing to try.