when i look onto the pictures i can see many little rustpoints which came from metal through zinga.
If u had seen the best way is with sandblasting in a preway and then with zinga.
I have had made same poor experience with several "top" zinc-coats from all over europe, but mostly with bad final.
At least i have found only 3 ways out
1. POR15 product = but here u have to follow up strictly the system, 1 fault = big + bad resulr and lost of much money
2. sandblasting + varmgalvanesering = much work, not the easiest way but best result over years
3. industri / technical paint/color, which is created for fast work and may with little faults with antirusting projects ( which is normal by standard users)
i had found out over years 1 delivery point where I can get rustprotection and filler in 1way, based on Epoxyresin, and also same basic-color ( normally produced for machines and also bridges etc in agressive (air) zones) in all RAL-tones. But the minus is that the producer didn't have any clear-color ( for technical paints its not necessary) but instead u can use standard clearpaint from Standox etc.
i had used also this primer on galv plates ( 5days ago galv with 450°c ), slib / grind with 400er paper the hole body, wash with little ammoniak-mix + no prob with primer or color after this short time.
If u want i can send u some technical dokuments ( sorry only in German) and i also have some samples at my place.