[falloutboy]

I cleaned my out as good as I could - had heat issues in city and stop&go traffic.
Since then the needle behaves like yours, but the car takes about 10 min longer to get to temp in the winter than the years before.
So yeah, cleaning and getting the scale out improves on the heating issue.

If I were you, I'd keep an eye on it, and see if it gets worse this year especially under hard circumstances (hot, humid, slow traffic).
If yes, try to clean and de-scale your cooling system.
For know, you could pressure test your system and see if there might be an issue.
Weren't there reports of hair-cracks in the coolant reservoir?