Well it's commonly accepted that Krillin is stronger than Tien during the Cell saga, it's one of the main reasons some people think that Krillin perhaps is stronger than Tien end series because people were under the wrong impression about Tien after Cell was killed and the filler line "I have no reason to train" or w.e(aside from the whole Yamcha statement).
So people assumed that they both slacked during those years, thus the statement Krillin > Tien held water, because Krillin was strong than Tien in the Cell saga.
It really just goes back to Krillin getting the Guru boost, and Tien not. From there on till Cell appeared, they did about the same amount of training, but Krillin would stay on top because of the Guru boost.
It's just, in my personal opinion at the Buu saga and end series that Tien is stronger because Tien had no reason to stop training, because he was never shown that he actually did, unlike Krillin who settled down and became a family man.