You are right about frame format. Most probably, while converting from 802.11 to 802.3, source MAC address differs so batman is not working with WDS. (can not recognize advertised interface MAC address??)
Now, packet performance issues arise. I suspect on MTU, fragmentation related issues through cascaded/nested structure of bridge/bat0/link system. Will need to dive into monitoring/capturing (as you also mentioned) this system. For example, streaming continues for a while and then stops. Simple restart of networking system solves the issue. If you have have a clue, it can help a lot. I will consider opening a thread for this.
Best regards,