I am not sure why most spec skis are so unstable, other than they are for racing, thus are mostly used by experienced paddlers who need that extra leverage by sitting high, leaning forward, if they want to compete. I have two specs. The Findeisen Stinger is very tippy, barely anything carved out for seat. I need clean conditions (not flat since in the surf) to use it. My Fenn Tarpon S, on the other hand, is very stable because of the deep seat. I’m not sure if Fenn makes the Tarpon anymore after the fire, but it is stable (the deep seat version). There used to be a Hayden Fatboy that was known to be very stable, but not sure if they are still made. There are other stable specs with relatively deep seats.
KR McGregor Rhythm, V10Sport, Swordfish S, Fenn Tarpon S, Fenn XT, Twogood Chalupski, Findeisen Stinger spec. Had: V12, Stellar SE, Huki S1-X, Burton wedge2, Fenn Tarpon