IT could take a millenia of book-reading and hashing out polemics to cover and dismantle this issue.
My own opinion and suggestion to support it is this: look at the history of the usage, the history of the schism, and the theology of the filioque and then examine weather this is a CAUSE of the split, or something to fight about.
I don’t think the theology is heterodox. What is more, and I am about to get myself into trouble, for all the protestations made on the part of some parties in EO - we were in communion for three centuries almost with local churches in the west adhearing to this clause - a response and clarification to problems those local churches were struggling with. Try mightily as some may to mine evidence of wide Eastern protestation, or to subsequently develop a theology in tacit rejection of the Filioque, I just don’t see it.
“The big deal” of it all could be debated for a lifetime with scholars who forget more on a wednesdsay afternoon than I will ever learn… But all things being equal, I just can’t subscribe to the notion that this is a “deal breaker” or “heterodoxy”.