As others have said yes you can hit 40 yard flops.
You can do them with PW's (to your point I have done them with both my 48* cleveland 588 and my nike vrs forged PW)
You can hit a flop out of rough if you use previously discussed PW's all about assessing the lie
And to mother point you made they never said decelerating they said "full back swing with a slow swing" I watched it a couple times and to me that's a big distinction as decelling and slow deliberate swing are 2 different monsters slow swing can get you a nice high soft landing but not as much back spin. Decelling can cause only headaches lol