It doesn’t sound like they did a good job and so the worry is that it could peel especially once you coat it with gloss. A lot of paints don’t need an undercoat these days, Zinsser Allcoat is my external paint of choice as it doesn’t need a primer or undercoat. However it maybe worth considering swapping the down pipe, they are not that expensive and if you can get it in the colour you want it could save you a lot of hassle?