Yes, i agree that that’s an important difference. I might even force different names for them, even though they kinda officially have the same name.
If you want to be pedantic enough to distinguish between aunts/uncles by blood and aunts/uncles by marriage, then you need to either use a language other than English, or add a bunch more words. The English words aunt/uncle/niece/nephew do not distinguish between relatives by blood and marriage.
And you’re probably not nearly as pedantic as speakers of some languages. In some languages, the words translated in English as “aunt” or “uncle” can depend not only on which parent they’re the sibling of, but also on whether they’re the older or younger sibling.
In Singapore, “Aunt” is used for older women. How much older depends on how young you are. Getting called “Auntie” for the first time by the young check-out operator in the store …
In Australia, “Aunt” is used as a term of respect for elders in the first-peoples communities. Most of the people using the word only speak English, but it derives from the fact that English doesn’t have words to match the language words for specific relationships in traditional first-peoples societies. Those languages also have terms for specific, and culturally important, distinctions between different kinds of nieces-nephews.
I call all my n-n nieces-nephews. Within the family, some of them are generally referred to by words that translate something like “older brother”, “number one son” etc: English doesn’t have dedicated words for those relationships.