mega hand strength really comes from the wrists (hello limp wristing), wrist curls as well as the grip master are what you need to be doing to improve hand strength.
As for the Glock, it's got a chunky grip and if it's too large for your hand it's going to be hard to get a proper hold on it. The 19 is also going to have a heavier recoil spring than a 17 etc. which will hurt cycling where limp wristing issues are present. You can try a reduced power spring from Wolff and see if that makes a difference, however the felt recoil may increase. A grip reduction on the gun might also be in order (or try a Gen 4 when they come out)
Arm extended and from the hip/chest retention are all positions you should be working on. When I shoot one handed from a "combat stance" I am still squared off to the target with my right arm extended and wrist slightly canted to the left let your hands have naturally at your sides and raise your right arm up and you'll see your wrist is slightly canted. Also work the one handed stance with a bent arm.