And you don't end up recovering better doing less lengthening, you end up recovering faster - there's a difference.
This statement is most likely completely false, i understand that you want to believe that it is true to justify the ammount you lengthened, but lets get realistic here.
The one source you posted did not mention anything about the actual ammount of cm the patients where lengthening. The claim that they didnt found any correlation of recovered muscle strenght to the ammount lengthened wouldnt be surprising if the patients in the test had a lengthening range of 3-6 cm for example. We dont know if any of them went beyond the mentioned safe limit or how much it varied between patients.
Also this test does not take into account how active or athletic the patients where before the LL process, if they where all average joes who werent active in sports, which is likely for at least some of them considering the age range varied from 13-57, then it wouldnt be that hard to reach their previous ability since they never pushed their limits previously either.
However someone who is very athletic and has pushed his body as much as he/she can before LL surgery would most likely notice that that previous level of athleticism is not reachable after doing LL, at least not if the lengthened ammount is over the safe limit. How much of a difference depends on the individual.
Finally these tests (the dynamometer and the leg extensor) do not test the patients agility and mobility of the legs after LL, which woud certainly be affected since we change the biomechanics of the legs by lengthening them (femur LL changes the mechanical axis, and also the femur-tibia ratio would change unless you lengthened them both specifically to keep the ratio, which would be very hard to do if you did 10 cm on tibias..