In addition to Orthodoxy's relative obscurity, one word regarding authenticity: contraception. (The salmonella in the analogy above.) Who changed?
Everyone changed, unless you're content to keep your eyes focused on documents and not look at the people in the pews communing with you--then you can say that the RC's remained authentic. But even if you only look at documents, I don't know of any document with the same weight in Orthodoxy that HV has/had in the RCC which made an official change.
What I see, in Orthodoxy, is an acknowledgement that this is a pastoral and not a dogmatic issue. The way some Catholics go on about it, the condom (as with all "artificial" birth control) is more of an intrinsic moral evil than the atomic bomb because at least that could theoretically be used in a "just" war, but there's no justification ever for a rubber. Only Roman Catholics could take prophylactics and build a theology around them. That's why comments like "reductio ad vaginam
religion", even if they seem distasteful or "mainstream left", aren't entirely off the mark.
Anyway, there are a lot of "one words" regarding authenticity that could be lobbed at the RCC. Your appeal to the decades of American Catholic history with the Tridentine Mass (with its post-Vatican II abrogation, allowance, and then retroactive non-abrogation allowing one to say it "never disappeared", again, all on paper) as opposed to the post-Vatican II situation (which you admit seems to argue against authenticity to a degree) is, in a way, an admission of guilt.
By the way, most ethnic Orthodox are deafeningly indifferent to abortion.
Most of the ethnic Catholics I know are similarly indifferent. It has to do with being "ethnic" in a foreign (adopted) country.
Ethnic people, in my experience, care about working hard to provide themselves and their children with a better life. Political activism, pro-life, hobbies, sports, etc. all get sidelined in favour of this main goal. When I was young, I was never allowed to play sports, take music classes, or become a scout because that would require parental involvement that would conflict with their work schedules (and they weren't uninterested in such things as others clearly were). Now, if I have children, I can see the value in providing those experiences for them, but my parents were too busy to provide those for me: they were trying to give me a better life than I would've had in what most Americans would consider "the jungle". As important as it might be, you're not going to get a lot of ethnic people interested in pro-life activism when they're exercising their own form of pro-life activism--pro-their-own-family-life activism--which is not always and everywhere equal to selfishness.
That said, I know personally of a case where an "ethnic" couple (the guy was Catholic, the girl was Orthodox) were having twins, and something went wrong at ~20 weeks. The doctors were recommending terminating the pregnancy, and so was the guy's very Catholic family. The girl's Orthodox family basically laid out all the options for them and told them to pray about it, that only they could make that decision, and they'd have the family's support either way. They decided not to terminate, to the consternation of the Catholics. One baby boy died a week after delivery, and the other is about five now, and he has made progress his doctors consider miraculous considering how underdeveloped he was when he was born. His parents went on to have one healthy child and another on the way. It was the support, moral but also real life assistance, of the Orthodox family that gave the couple the strength to go through with having the twins in spite of the dangers. If the Catholics in this situation had their way, the now-five-year-old boy would be dead too.
Life is a lot more complicated than your easy stereotypes.