It should be noted that the blast zones' distance referenced are probably being estimated at the extreme edge of the main Stage platform. Helicopter Kick may not KO earlier when calculated from more mid-distance locations and Piston Punch would probably come out as a better KO option from platforms above Stage, especially considering 4 of the 7 most commonly used Stages have significantly elevated platforms and 2 others have not-extremely elevated platforms. Two of these commonly used Stages also have shorter-than-average ceiling KO areas (Dreamland and Town & City). Bringing Delfino and Halberd into the equation (which I heard may be used at Evo2k16) really brings out the KO'ing potential in PP.
Keep in mind that some characters may be KO'd out of the top area easier than side areas and also the setup into these moves are a thought factor.
As far as recovery options go, the Feint Jump offers supreme horizontal recovery and suppliments PP excellently both for distance and mixing up timing/area recovery options. I personally run Burning Drop Kick with my Piston Punch, doubling up on horizontal recovery.
In summary, I have used PP since day 1 of Japanese 3DS release and still run with it.