I don't know the answers to all that. Also there is a shadow weave, that shadow magic uses instead of the regular weave.
Other Gods, particularly Bane, Cyric and Talos were jealous of Mystra because of the power she wielded as god of magic, but they were not subservient to her. Also just because she tends the weave does not necessaroily mean they couldn't use it. Let's remember too it is past tense because she is dead now so the weave is I guess drifting about on its own.
Ok, as far as I know the weave was infact created by the Goddess of magic and Shadow weave is another analogue, but both are interfaces through which mortals can use Magic, since like I meantioned using magic without the weave is very dangerous for mortals. When the Goddess of magic created the weave there were rules put in place, spell slots is one of those rules for example.
I would prefer an answer from someone who knows for sure, but I will accept speculation that also makes sense, so long as it is a good explanation. So if you are saying that Weave is in infact magic and not an interface to use magic safely, how would a God other than Mystra use magic without her blessing if she has direct control over weave?
I just don't read 5e materials, don't buy books, so I gather information through video games and some bits and pieces online.
