Did I need to spend so much money rebuilding the torque converter and replacing the radiator? Or simply doing a transmission adaptation would have taken care of the problem?
Thank you in advance for any thoughts about this.

I would say no, the radiator and torque converter replacement was probably for naught.

Sometimes that's the way the cookie crumbles, if it were me I would speak to the shop who did the work and see if they will refund a portion, couldn't hurt anyways. One would think an experienced repair place would have a way to test for water in the ATF. Personally I would not have had them replace the radiator and converter without being sure there was contamination. But hindesight is 20/20. At least your car is sorted now, still less than a trans rebuild right?