Well, after reading this thread because I found myself in a similar position to OP where I felt like a total failure with this aircraft, I'm actually feeling much better about things. I only picked up the Mossie a couple of days ago, and I've spent a frustrating amount of time spinning and exploding in flames trying to get the bird off the ground.
But now I'm reading about how difficult the Mosquito was to fly in real life, and that most - if not all - other Mossie pilots in DCS have experienced this massive learning curve. And that's great, because it means I'm not alone. So now, all I want to do is keep practicing. It's changed my mindset and increased my confidence and determination. So much so, that I've just successfully completed my first takeoff, took a short flight along the Kent coast, unloaded the cannons and machine guns into a few ground targets, and RTB. Unfortunately, my landing didn't go as smoothly! So I'll keep trying!
Huge thanks to those who have shared their tips and advice!