Disagreed. Anyone who states that physics has "no problem-based projects" has obviously never built a neutron detector and implemented it in Notre Dame's particle accelerator lab investigating high-energy nuclear reaction studies - something I did during my time doing research as a physics undergrad. Also, the implication that something is easy unless it is a problem-based project is ridiculous. Say that to a theoretical physicist and... Well, he/she probably won't have the physical prowess or upper body strength to do you much damage, but they would write you a violently-phased derivation of Schroedinger's that would make. Your. Head. Spin.
Seriously though, I have majors in Physics, Chemistry, and Spanish, with a Math minor, and the upper level Physics classes were conceptually the hardest classes I have ever had in my life - particularly Quantum Theory. We got four multi-part homework problems each week in Quantum, and each problem would take 4-8 hours to complete. Of the ten physics majors in the class, two dropped and four had to retake it. The class average on every exam ranged from 40%-60% - and these were people that were simultaneously acing Organic Chemistry, Biochemistry, and misc. engineering courses. Our professor started the class off by stating that it was the hardest class offered at an undergraduate level, and nobody ever disagreed. Also, I had friends who doubled in Physics and Engineering and regularly said that the Physics major was the more difficult of the two.
As for whether it helped or hurt - as long as you are well-rounded and show that you can do well across the board with the premed courses and MCAT sections, it will only help. If all you are is a Physics major and got crappy grades, it'll probably hurt you, but that is true of any major + poor grades combination. Standing out in any positive way is always good, and there is no way that Physics is a common enough major for med students that it would help you blend in. I know there are other Physics-descended med students out there, but I have never met one in person...