This may just be the Guardian's wording of the data source, but it makes it sound more like the real conclusion is "parcels currently being delivered by cargo bikes are better suited to delivery by cargo bike than by van".

The subheading does add the caveat that they were only looking at city centres, but I can't help that think it's a little ungenerous to ignore some of the areas within city centres that vans might potentially still excel (eg: bulky items)