The idea that a posterior pelvic tilt in a hip thrust will increase glute activation is a myth promoted by YouTube gurus who try to get attention by adding bells and whistles to exercises. This study finds that the pelvic tilt approach, which is called the American Hip Thrust, does not increase the activation of your glutes. The lead author of the above study is Bret Contreras, who is the person that has popularized hip thrusts over the last decade. This study uses EMG measurements, so his results are probably robust.
Another key point that Contrears makes is that the American Hip Thrust (the version with a pelvic tilt) is a more complex movement because one must be able to control the pelvic tilt. In another study, it was found that over 50% of amateur weight lifters executed their deadlifts with poor pelvic control, and they didn't know it. So if you are practicing the American Hip Thrust, keep in mind that there is a 50% chance you are not executing the pelvic tilt properly.
As far as "protecting your lower back", Contreras states that "individuals with extension-induced low back pain may prefer the American hip thrust, as it involves PPT [posterior pelvic tilt], which reduces the risk of lumbar hyperextension". However this is one sentence buried in a six page paper, and it is asserted with no evidence. Back pain is not studied anywhere in the paper. At this stage, the above statement is nothing more than conjecture. In my opinion, the above statement should not have been included because it is not connected with any thing else in the paper.