I gotta thank you all for your suggestions on how to fix my bathroom trim. Not only do your ideas take care of the problem, they’re easy fixes. That’s a win-win.
When I asked last week for ways to fix my bathroom trim, I was confident you’d come up with some good ideas and you did. The best idea, in the sense that I never thought of it and in hindsight seems like it should have been obvious, is a simple threshold for those doorways.
The best part is that it’ll take only about 10 minutes to try it out to see if it works as well as I think it will – just plane a piece of scrap stock to fit under that doorjamb, bevel one side, and slide it into place on one of the doors. If it works and looks good, I can cut a real workpiece, paint it to match and do a permanent install, then fix the other two doorways (another in the master bath that goes to the walk-in clothes closet, and the entrance to the upstairs bath).
That still leaves one problematic doorway, the one to the water closet in the master bath. That one doesn’t have carpet on one side – it’s a smooth continuation of the flooring from one side to the other – so a threshold won’t work there. Instead, I’ll try slicing some 1/2" pieces of matching molding and glue them into place, then take several commenters’ suggestions to use Bondo to smooth things out.
In the process I’ll gain a new woodworking skill: using Bondo. Never worked with it before in my life. However, it rhymes with “Play-Doh,” so I’m thinking it’s probably pretty intuitive.