From my experience with the A pillars on my 3 year old 4/4 as you have found a repaint or even powder coating will quickly start to
flake away for the reasons mentioned by PeterJ.
I took another route to resolve: I sanded down to bare metal in situ and had the pillars wrapped in black vynal at local depot for £40 the pair..only took 40 mins..much more durable.
The base must be super clean for a good job.
Finished job:
