I saw 633 Squadron when I was a child, before developing my awesome critical faculties[sup]TM/sup, and loved it. The clichés weren’t clichés to me, and I knew nothing about quality acting or directing. Even as a kid, I realized that there was something special about the Mosquito. I doubt that I’d watch it again, because I would probably cringe at the faults that you list. If someone puts together a montage of the flying scenes, I’d watch that.
However, it’s almost certainly not the worst Mosquito movie out there. A couple of years ago, I caught the execrable Mosquito Squadron (1969) on late-night TV. At first, I thought it must have been a showing of 633 Squadron (with the name changed for the US market?), because so much of it seemed familiar. Then the plot started to diverge, and I couldn’t remember David McCallum being in the version that I’d seen as a child. As the film got worse and worse before my eyes, I realized that it was a horrible recycled semi-remake, using a great deal of 633 Squadron’s aerial footage and much of its plot! The final target was different (they used Barnes Wallis bouncing bombs on land!, which makes it the evil hellspawn of both 633 Squadron and The Dam Busters). I think that there was some new Mosquito aerial footage, so it might be worth a Netflix rental, but otherwise it was a shameful waste of film.