Cars have always been slowed down by rule changes, and then the designers have managed to speed the cars up again. Off the top of my head, to slow cars down over the years they've banned: turbos, double-diffusers, ground effect skirts, active suspension, automatic gear changing, large front and back wings, aero winglets, slick tyres, slotted/profiled undersides, blown exhausts, exhaust gases as downforce generators, etc. By the end of the season they are usually as fast or faster as the previous year. This year is no different, but we've seen so much stagnation, a big rules change has shaken things up more than usual.
I read somewhere that one of the reasons for the fuel flow limits was because otherwise the engines could potentially put out 2000 bhp, and there would be dangerously massive difference in car speeds if people turned their engines up and down during the race.