1) The RCC is certainly not united in its doctrine among its practitioners, no matter what it would like us to believe. - According to you, but not fact. Show me one DOCTRINE that members of the “RCC” disagree. True members, not those Rainbow Sash freaks for example.
2) The RCC changes its doctrines to suit the times and temperament of its magisterial class of law-givers. - That’s one interpretation of what happens in the Church. Another, is that the understanding of the original deposit of faith at Pentecost is clarified and brought to fuller meaning. Both are valid explainations of what the Church has done over time but...
Worth noting, the former position (the RCC changes its doctrines) is a rather pessimistic if not sarcastic view.
3 & 4 are all very nice sounding and feel-good, however it doesn’t really address the reality of the passage in Matthew, to whit, there can only be one Church of Christ’s. I still submit that to say this one Church has disparate doctrines is, well, quite frankly, universalism.
If those "Rainbow Sash freaks" as you call them aren't at a minimum being denied the Eucharist, i.e. aren't having their self-excommunication acknowledged and enforced by their own bishops, then I am forced to side with those bishops and to disagree with you - those "Rainbow Sash freaks" are still fully communicant/true members in good standing of the Catholic Church. And that means that their doctrines are your beliefs, too. After all, your respective bishops think you're both good Catholics.