Here’s a puzzle! Lesson 25, Level 2 (Gog) seems to use two forms of “would” in the same sentence: Byddet ti’n helpu ni, faset ti?" “You would help us would(n’t) you?”. Which is a bit confusing.
Also, I’ve been told by a Gog speaker (Ynys Môn) that the byddwn/byddet/byddai form is used for something done regularly: “He would play the drums every weekend.” Whereas baswn/baset/basai is conditional: “He would play the drums next weekend, if he had a drum-kit.”
The two sets are certainly interchangeable to some extent, although I was told during my Welsh course at university that it is ungrammatical to mix them within the same sentence… however, spoken language (and this is not confined to Welsh!) is often ungrammatical in practice, so you will come across mixing.
Your Gog speaker from Ynys Môn is correct - the byddwn set is indeed also used to describe a habitual action in the past, whereas the baswn set is not used in that sense, but both can be used for conditional.
It does seem confusing, but the more Welsh you hear and use, the more your brain will begin to make links as to which is used when, so try not to overthink it, go with what comes to mind first, and don’t worry about getting them ‘wrong’ because you will be understood even if your brain hasn’t processed the nuances yet.