How to get flour quesadilla light and crispy?
I use a liquid oil instead of a spray oil; you're far more likely to get hot spots with a spray, which is bad for any kind of cooking. That stuff works better as a grease than an actual cooking oil.

I also tend to have pretty good success by frying the tortillas up to just a hint of golden-brown (dark brown spots is overdone) and then finishing it off (i.e. to melt the cheese) in a low-heat oven. As an added benefit, if you're making a largish batch then that makes it easy to keep them warm until they're all ready to serve.

YMMV, but I find this to be the case for a whole lot of stovetop cooking; with the direct heat, it's very easy to dry foods out before they're cooked to the stage you want. It's far easier to control the heat in an oven and just use the stove for an initial (or final) fry/sear.