I loved my Clipper, was my favourite ship. But then Horizons came, and the buff to the FDL made the Clipper into a big clunky target drone. In PVP the Clipper just can't compete anymore. The FDL is tougher, tankier, punches better and is nearly as fast. For Hull Tanking, the Clipper do a decent enough job, but why bother when the FAS does it much better - and have the same weapons-layout only much better positioning of the hardpoints?! Oh, and is nearly as fast.
The Clipper do have speed, but now that is all it got. In every other respect (in PVP), it is inferior to the FDL and FAS.
As for the Python, the SCB heat issues have put quite a handicap on the ship. To tank effectively, one need give up a couple of Shield Boosters in order to make room for Heat-Sinks. Which means if the Python get focused, it'll lose shields and die before it can get away.