Engines aren't designed with pure piston + crank + transmission + gas = power, anymore. If an engine system is designed with an EGR valve in mind from square one, then it will be better, and run as intended, with the valve in place. If it's added on after the fact to an older design, I would agree with you, but not this time.
For instance, on my car the EGR valve is there to help quicken the warm-up times, give me better fuel economy, decrease heat wear under moderate sustained loads, and just in general increase engine longevity by decreasing detonation and letting the engine respond to fuel/air/moisture conditions, which save cylinder and ring wear that would occur if those problems were attempted to be helped with other means. It also lets my engine give pure power when pure power is due and needed, without compromising daily driving performance and stability. All three valves on my EGR are closed at WOT and at other times when I need pure power. It's not the simple dumb system it was, purely to meet emissions. Now it should be thought of as more of another intake system that cannot be disposed of willy-nilly.