I have also been a bit unsure at how much protection they really offered.
From what I understand about masks protection would only really work if everyone wore them correctly.
That has never happened because some people were exempt, some people didn’t practice the correct hygiene, some many people didn’t wear them correctly, plus there is a lot of uncertainty as to how much protection reusable fabric ones provide.
So, for the most part I always just assumed masks was more to make people feel they were doing something, rather than actually doing something.