But when did you last have to give way to an oncoming cyclist at one of these road obstacles?
Any time I consider that there might be a danger that I might come into contact with them.
If you pass a stationary vehicle or object, you automatically move out to stay away from the door zone, or that somebody or something could emerge from the blind side of the obstruction like a ssmall child or dog (etc), so you need more space than your physical width to pass safely.
You don't just demand right of way over traffic in the oncoming lane just because you are physically narrower (do you ?). That is their space and you have to respect that irrespective of what you ride or drive. If they choose to then give that up that right and let you though, that is their right to give, and not your's to demand.
This is how I see it, and what I expect others which I share the road with to do, whether I ride a cycle, motorcycle or drive a car (4x4 or otherwise)
The OP does state that they stayed on their side of the road so I take that as the Merc driver having a bit of an inconsiderate 'I own the road' moment