Technically there are initialisms which cannot be pronounced ( letters only ) and acronyms which can be pronounced ( form words ).

So, in general, your rule is a good one. Of course, that does nothing to solve the problem of HOW to pronounce the words when so many different origin cultures are at play. As other have said, SUSE is German. So, is following “English grammatical rules” the right take?

I do not really have an answer. It is not self-evident to me. For Linux, Linus himself seems to have defaulted to US pronunciation. There is some precedent there I suppose.