The DPF and SCR systems are new (few years old) technology and as usual the "baby teeth" are highlighted on Mercedes brand, when the same issues on Fords go unnoticed, as parts failing on Ford are expected.
Transits don't come with diesels, so their engines have different problems, but fact is that it is easier to find mechanic for Ford (not necessary qualified) than for Mercedes.
It all boils to regional market. I noticed that in California, NY, Chicago finding good MB mechanic is not an issue.
But try find good MB service in Nebraska, or Alabama?