Most microwaves will not reduce their power. They will reduce the percentage of time the power supply or the magnetron is active. In other words, longer rests in between shorter blasts.
The actual microwave "heat" is applied in a fairly narrow beam (about 2" in diameter). This is why some microwaves have a turn table. So, placing the food off centre is better.
When part of the food gets really hot, it starts warming up the surrounding parts as well and eventually reaches a sort of an equilibrium.
If you have a thermal imaging camera, you can place a damp paper-towel on a plate and see the heating pattern for yourself. This is where you can do the rigorous experimentation. While I did use scientific equipment in my tests, it was just for my own curiosity.
When you run the MW at 100% you're overheating parts of the food to help warm up the other parts of the food. Overheating food has a great chance of reducing flavour and breaking down some of the longer molecules. Usually, the water in the food buffers this, but it does depend on the what you're heating up.
To answer your question, yes, you are better off reducing the power. Regardless of the total wattage of your specific microwave oven
Running at lower power, reduces the peek temperature of the areas that are blasted by heat. Yes, it will take longer, but you keep the temperatures of parts of the food more even.
Again, if you're really curious, warm up food in short time intervals and take a look it with a thermal camera.
You may end up opting for a toaster oven after you see it all.