In this very thread, back in October, Garyh550 shared a link to a similar discussion on YouTube Help Forum, and two posts before last (sorry, can't link to the actual post, but the topic is closed and the post should forever be two before last) JNPR_boy offered a solution that I just successfully tested. Deleting the YouTube app & restarting the iPhone brings back the icon to the Share menu in the native Photos app; sharing that way is also wicked fast (and still asks the usual question about title, description, quality, privacy, etc.). Put YouTube app back on that phone, and puff! that sharing option directly from the Photo app is gone.
This confirms what the original poster already heard from Apple Support: it is Google, not Apple, who decided to remove the sharing & force users to use the YouTube app.