Warped rotor on my Kawasaki?

[WuzzaCBXRider]

As I approach 28,000 miles I find that my front left rotor may be warped. On track stands the wheel will barely turn by hand but when I remove the caliper it spins freely. The pads are relatively new and in perfect shape. I’ve felt no pulsing under braking (it has ABS) or any other issue with them other than it’s harder to push around the driveway. Any ideas other than rotors? Some years back I switched to Arashi rotors on my Busa and they’re great. Could it be something other than a warped rotor? I suppose I could buy a micrometer but after removing the caliper which freed up the wheel, what else could it be?

 

[Dnyce]

Caliper pistons sticking

 

[WuzzaCBXRider]

Caliper pistons sticking

Well I thought of that but removing the calipers was easy, they slipped right off and went back onto the rotor just as easily. And I’d just used the brake before putting it on the stands. So, calipers easy on/off, pads fine and when placed back onto the left rotor and bolted w/o pumping the lever, the wheel is very hard to spin. As I spin it it becomes easier as it rotates and then back to being hard.