most production shops are looking to give a 1yr type of product.
I redo a ton of powder coating from 2 off road manufactures after 1-2 years

typically only chemically pre treating parts, which werkz well... same as anything else if done properly. Most vehicles on the road today for the past 10-15 years have been chemically pretreated, and it shows. factory paint jobs last longer than pre mid 90's.

chemically pretreated parts done wrong, or poorly (worse than wrong) are the same as no pretreatment. In some cases worse because a coater could easily poorly pre treat a product, have the item rusting almost immediately as a result, then coat over the rust.
Which sounds similar to what you are/were experiencing.

The best results I know of currently is for a part to be mechanically abraded, preferably media blasted, the Phosphate coated, sealed then the finish applied. This werkz with paint or powder.

Once the substrate is properly pretreated to accept a coating, it is then a matter of the actual coating performance. If one has 2 identical parts, pretreated the same exact way, no variance what so ever, except coating. Powder out performs most wet paints in durability, and cost. Usually I can powder coat say a car frame for the same cost as quality paint materials.

then the benefit is client "X" had their frame blasted, pretreated, and coated for $500-$700. Where blasting, pretreatment if one can get it, and then quality paint supplies would easily cost the same, then customer "X" would either have to apply the paint, or pay someone labor.

Like I said, I'm not saying powder is the best thing in the world, or is for every application. It is usually a superior product when applied properly. I hate to hear about instances when it hasn't been, and fails prematurely.

Sharp edges always cause edge pull, paint or powder, and weld seams are usually moving joints on bumpers. Blasting, and lightly filing the sharp edges usually cures those issues. for a manufacture it's an extra cost, and some company's don't care if it last one day past the warranty sadly