There are every year lots of boring races. Always been there, always will.
I don't see the 3PU rule as a reason. What I do see as a reason is the sophistication of design. The cars, especially the cooling, is designed without any leeway. After a few laps behind someone and your PU becomes too hot. They could enhance cooling, but that would cost laptime (for qualifying for instance).
Next to the cooling, the details of aero are so sophisticated that a small disturbance (as in turbulence from a car in front) will negatively impact downforce.
It looks like that cars are more designed to qualify then to race. Maybe we should go to qualify aero packages instead fo qualifying engines? (other FW, suspension settings and RW settings)