I would leave technicalities for coaches but I can tell you from my own experience, my backswing was always big 'cos that's how I've been playing for nearly 30 years. The problem is with faster ball exchange, where I tend to get a bit late. Shorter backswings in modern shots make strokes more compact and it's relatively easier to deal with faster paced balls. I'm in the process of rebuilding my forehand but it's not that simple to remove something that's been ingrained for years. I keep trying though.