Some are definitely based on surf skis others or at least inspired by them.

I have a Panthera and also a Think EZE surfski (a 'beginner', not 'race' surfski) and there is really nothing common to the feel of those two boats.
The Panthera feels a lot like my Frej in terms of stability/edging/handling rougher conditions - i.e. like an excellent sea kayak.
The surfski - not at all the same...I need the paddle in the water to stay comfortable and the secondary stability is nil.

When Bjorn Thomasson was developing the Panthera drawings, I recall from our emails that part of the 'design mandate' was the kayak-like stability/feel.

The Panthera is quick and the rudder keeps it tracking straight - without the rudder it is quite easy (much easier than my Outer Island) to turn. The EZE is quick and needs the rudder to turn.

Some of the difference in feel between Panthera and surfski may well be the lack of a deck on a 'ski which pretty well takes the knees and hips out of action for keeping the boat upright. A more expert paddler than me might have a different 'take' on the differences.

BTW, as Ron says the Panthera can 'swallow' a lot of gear, though I try to resist the temptation to put much up in the bows.