When you actually here the ex salesman of someone like Citroen say don't buy one there trouble you tend to sit up and take notice,when the mechanics say the same would it not put you off slightly. They have more vans in for repair under a couple of years old than other makes just getting a service,you are bound to get a batch that don't get as much trouble it's the same with anything but you have to look at the overall picture that's what a magazine like whatcar do they wait a few years and then give an opinion.
The problem is NWH that your original post demonizes all French Diesels - (speak to any good experienced mechanic they'll say if it's diesel and French don't buy it.) - The French led the World in making modern diesels refined and acceptable after the ghastly, tractor like stuff of the past. The PSA XUD were the first really refined, mass produced diesels with VW making the first high speed diesels The French, or specifically PSA, were so accomplished in their manufacturing skills that when Ford finally admitted they didn't really have a clue it was PSA they worked with to find a solution - using Ford money and PSA know how.
As to the very modern vehicles that you now mention then the problem most likely comes from all the anti-pollution stuff that's been nailed on by successive legislation which is making ALL diesel engines overly complicated and ultimately unreliable. I've a friend who works for Volvo and he attended a days course on the problems and issues that will be presented by the new environmental requirements on the new XC and says it's daunting,
Possibly now the only way to run a new van is simply to find a good lease deal and let someone else worry about any likely issues.