There is a mix. There are unbiased studies that look at multiple shoe types. They tend to focus on broad categories (e.g. mid sole) or spcific material (e.g. high density foam). The studies that assess proprietary technology are often biased. Even if they hire third party researchers, the studies are often designed to guarentee success.

You need to look at the bigger category studies and look through the conflicts of interest. The study design matters a lot as do the interpreteations of the conclusions. Look for numbers and the magnitude of effect (effect size). Non-significant differences or small effect sizes don't translate into real world results.