If your purpose is, as stated, to get a deeper understanding of SR then this is irrelevant. It does not matter in the slightest who contributed what not how one scientist’s contribution compares to any other’s. A deep understanding doesn’t come from learning the “Trivia Pursuit” parts of the theory.I am trying to get an understanding of what Einstein's contribution was in order to get a deeper understanding of special relativity. I don't doubt his contribution was major. I just don't understand it, and can't say what was it that he contributed compared to what Lorentz did, or what any other person did for that matter
If you really want a deeper understanding then you need to look at modern treatments. In particular ones based on symmetry principles.
Edit: I see that the point regarding history was already made. However, I will reiterate the point about symmetry principles. Today, a deep understanding of physics is about symmetry.