There's no difference in rider fit between "classic" and "compact" style frames. Only the slope of the top tube is different. You could make two frames that put the rider in the exact same place, one with a level top tube and one with a sloping top tube. There are of course differences in fit between different makes and models of frames but the slope of the top tube does not cause that.
There are arguments for each style- the sloping top tube means a longer seat post which has slightly more give (depending on its diameter). Sloping top tube frames should, all things being equal, be slightly stiffer. But with modern carbon construction the designer can do a lot more tuning than they could with standard tubes, so that's pretty much moot. The last difference is standover height, which could be important for shorter people. But other than that, with carbon, the only real factor is looks. Some people are stuck in the past and like the level top tube, some people have more modern ideas of what a bike should look like and like the sloping top tube.
I'm in the no special bike for crits camp. But I wasn't much of a crit rider when I did them and don't race them at all now. Back in the day guys would have special crit bikes with higher BBs for cornering clearance, and shorter stays for stiffness and quicker handling. But even then I think that was just an affectation as the Europeans seem to race crits just fine on regular road bikes.
Power Transfer is a myth, dreampt up by marketing. In almost all cases it's BS. (If someone wants to argue this, please find me a study that shows a significant power loss due to flex. I haven't found one yet. Also, Sean Kelley Vitus 979 etc). A flexy frame (or any other part) doesn't make you slower, because it's a spring. When it flexes it flexes back, returning whatever energy it took to flex it. However a rider may prefer the feel of one vs the other. You'd think that a perfectly flexless frame would be best but it's not. Besides the jarring ride, you need some flex in the frame for traction. For example, when accellerating over rough pavement. If the frame flexes a little the rear tire won't skip as much. But basically it comes to rider preference.