The key here is that you’ll probably find the exact same “oddity” among speakers of other languages, even outside India.

I think British English put more and longer emphasis on vowels. It’s almost like they speak in vowels only. Compared to Canadian English, Indian accents are still fast.

I feel like you might have unearthed something interesting here.

The English varieties spoken in those countries like Canada, Belize, USA, Jamaica, etc. had plenty recent interaction with multiple local languages; specially Canada with French. On the other hand, what people usually call “British English” is mostly Standard Southern British (up/middle class, around London), a bit too far away from any meaningful linguistic influence.

So I’m wondering if the pattern that you noticed for Indian speakers and for the others isn’t actually the same pattern. I’m just hypothesising though, this might be incorrect.