Standover height always was a crude way to measure frame size even before the advent of compact frames. This isn't a new issue. I currently ride a frame that is 4 cm smaller than the frame of my first good road bike, and my current bike has a level top tube just like that first one. The point is finding a bike that is comfortable. I did a couple of very fast centuries on that first good road bike, under 4 hours and 15 minutes. I won a national level time trial on it. But it would probably be too big for me now, I can't stretch out the way I could then, because that was the only way I could be aerodynamic on my old bike. There is nothing wrong with a sloped top tube, it can help riders with short legs and long torsos fit on a bike. It just means that you have to do a bit more research when you look for a bike