It’s important to measure before and after results any time treatment is administered for orthopedic injuries. That’s especially true with athletes who are eager to get back into the game. Orthopedic surgeons and physical therapists testing this patient group must make sure they are safe to return-to-sport at a competitive level. Avoiding reinjuries is one reason assessment of motion, strength, and function must be performed.
Whereas the surgeon might say the case has been successful because motion and strength are restored, the patient who can’t return to sports play (swimming in your case) remains unhappy and feels the treatment was a failure.
Your own report that speed and endurance have not returned to normal is an important subjective (self-assessed) report of results. Providing a record of timed trials provides objective data (evidence) help your surgeon see that there’s still a problem.
You may just need additional rehab to get back what you’ve lost in terms of strength and function. Start with a return follow-up visit with your surgeon and this new information and see what he or she recommends. There’s no need to be satisfied with less than you expected until further evaluation is done.