I'm on many hiring committees and I try to evaluate quality of research as well. While you cannot spend too much time reading all these papers in full, just looking into them for a few minutes usually gives a sense of where the results fit and how significant they are. A good recommendation letter is useful here: especially for PhD research, the advisor can briefly explain what motivated the problem, how the result was found, what is its significance (from their own point of view of course), and what the candidate contributed to it. The reco letter can also explain why the candidate has fewer/more papers than usual, etc. At the end of the day, there are many objective-looking criteria, but in my experience people still make gut decisions based on their overall impression and then look for criteria to rationalize it. I find this to mostly work OK though, and better than having purely objective criteria and sticking to them no matter what.