I don't think it has made the on-pitch referees worse. However, it has basically given them a second job to do as VARs, which they are also (to varying degrees) not doing well. Which kinda compounds the problem of bad officiating as it adds an extra layer to it. Especially when the protocols around VAR are still very messy in the PL especially.
One of the interesting points in the article you posted above relates to that. As it says, some refs are just better at being VARs than others. And where other competitions might have a dedicated panel of people who can focus entirely on being VARs (and be assessed on how well they do that job alone) the PL are swapping refs in and out as VARs, including some from lower divisions. Specialisation would make more sense, you'd think.
Though saying that, I see Lee Mason is the first ref retiring to become solely a VAR....