That's not an opinion, that's how basic Slavic morphology/grammar works.

For example, some Russians say "v ogorode" ("in the garden"), while others say "na ogorode". We don't say "v" somehow got "distorted"/morphed into "na". Some dialects simply choose to use a different, unrelated preposition in the same context.

Are you trying to teach me Russian? Let your opinion be yours.

I'm not trying to teach you Russian. I'm giving an example in a language you're familiar with.

I can give an example from Germanic languages.

Old English: tōdæġ (modern English "today")

Swedish: idag "today"

Dutch: vandaag "today"

Same root ("day"), same meaning ("today"), but different languages chose different prepositions/prefixes (to-, van-, i-).

Just like with s- vs. za- in Russian/Serbian.