This is about the most interesting and informative PPrune thread I've read in a while.
Having sat in both seats, and now moving seats again shortly, it really has got the brain juices flowing.
OP, you didn't I think mention the outcome of your colleagues plan/decision i.e. did everything go according to plan and a safe operation continued VMC to touchdown etc?
Assuming as much, would it not have been worth a minute or two of reflection to get your teammate back on your side? I'm not suggesting abdicating your P1 responsibilities, merely that in a lot of cases its much more effective to nip any issues in the bud at the source with a sensible but concise de-brief. For me it might be as simple as
"hey mate/madam/dude etc etc, nice job, I now understand what you were trying to do, back there at 20 miles and 5000' I was a little unsure which is why I asked and why I made the suggestions I did. In future you might want to consider that the other guy/gal isn't on the same page as you. You and I both know that as P1 I am ultimately responsible for the operation so in that sense I'm just making sure I'm fulfilling our responsibilities to get our pax home safe and sound. All that aside, nice job again..and as its raining, you can do the walk around."
In my experience, the best operators (in both seats) I've flown with have been the ones who know when and where to fight the issues that crop up. From your description, it does sound a little like the PF was defensive due to not having as comprehensive a plan as yours, most likely though, once on the ground, instead of taking the opportunity to learn, they would have remained focussed on being upset/defensive rather than learning from your experience and more thoughtful and reasoned plan.