Well, without having actually been there, my impression is that in the EBTs we find a strong distinction between these things;
- teachings on rebirth in various realms, told in an abstract or general sense (dependent origination, etc.)
- narratives involving deities named or unnamed
The former is found attributed to the Buddha, the latter usually isn’t, but is part of the background narrative. People who discuss this usually ignore this distinction, and so tend to say either that everything is real, or that everything is “just myth”, using “myth” in the popular sense, i.e. isn’t true, rather than the narrative sense of “sacred story”.
However, I tend to take the things in the former category as being straightforward teachings and therefore probably true, while the second category are sacred stories told to give life and meaning to the former. In other words, the second category is certainly “myth” in the narrative sense.
In addition, I suspect that most of them are also “myth” in the sense of being untrue. The background stories on the whole in the EBTs are clearly less reliable than the doctrinal teachings, and many of the stories involving deities involve things that are obviously implausible for all kinds of reasons, even if you believe the gods are real.
Compare with the Jatakas. If you accept rebirth, then clearly the Buddha had past lives, and it’s very likely he could remember them. Yet it is very unlikely that many, if any, of the Jatakas are actual past life stories. There are just too many historical anomalies. So I think the stories involving deities are likely to be similar to this.