The TNG Galaxy will be able to beat the Intrepid if it was a gun fight. It's just too powerful and well armed. However the Intrepid is faster, smaller, more advanced and more maneuverable. It really depends who's the crew behind the ships. Look at TWOK, or TNG:Peak Performance. Additionally, The Galaxy class is still a relatively new class. They got a lot of life out of the Excelsior and Reliant Class ships, and had upgraded them a lot through time. It's reasonable to assume that newer Galaxy class ships will have many of the technological changes seen with the Intrepid class ships. The only fundamental difference would really be size, speed, and power.