I eventually caved and created a G+ page for my "channel". It is annoying how many times YouTube asked, but the result is quite satisfactory. The sharing settings actually seem pretty reasonable to me: whenever I interact with YouTube, Google is very clear about who will see my content (the "Public" icon from G+ is reused when posting a comment, +1s and upvotes are explicitly mentioned as being public, and so on), and having a "page" for my "channel" lets me not use my real name on YouTube, which I irrationally do not want to do. (jrockway is fine. A two-word Real Name is just too damn formal for trolling YouTube.)
Overall I do not think this is such a terrible thing; as someone who used G+ pretty actively before the comment system merge, I do see a lot of relevant comments on YouTube videos I never would have seen before, and since I would probably be sharing the videos I like to G+ anyway, it doesn't bother me that my comments show up in both places.
It would be interesting to invent a time machine, go back in time, and try doing the merge the other way: fold G+ into YouTube. G+ users probably wouldn't be mad, since they already use YouTube, and YouTube users probably wouldn't be mad, since they wouldn't notice anything changing. But whatever, the current version of the integration is fine with me, once you decipher what "page" and "channel" mean.