Is it true that blu diesel+ has a lower lubricating qualities than standard diesels?

No, that is not true. It is based on the false idea that in the past premium products had a lower level of sulphur content (10 ppm) than traditional diesels (50 ppm). As is well established, a higher quantity of sulphur increases the lubricating power of fuels.

Since 1 January 2009, in line with a European directive, both premium products and standard diesels must respect a sulphur content limit of 10 ppm.

Moreover the lubricating power is regulated by a European norm (en590) with a lubricity parameter that is kept specific also with the addition of so-called "lubricity improvers" to both premium and standard products.