From what little bit I've read, it seems that Thiele-Small parameters were used primarily to design a cab specifically for an EV speaker. At least that is possibly how the moniker "Thiele cab" came into popular usage. I have a Boogafunk "Thiele" cab, and it sounds absolutely huge and fantastic........with an EV speaker in it. Put a different speaker in there, and it shrinks back down to normal every day life dimensions tonally. IMO, if you dont put an EV speaker in there, the cab itself will not be all that impressive over any other well made cab.
Put it this way...... if you have one Thiele cab and you switch out several speakers, the cab will not be all that impressive. But if you go the other way and have one EV speaker and change it among several different makes of cabs, then the Thiele "made for EV" cab will be very, very impressive. I personally think my Boogafunk cab improved the sound and capability of any speaker I've had in it.....Webers, EV's, Tubbys. I agree it is most impressive of all when played together with a second cab. But if I were forced to pick one cab to keep and trash the others, I would keep the Thiele, no question.