That´s true. But I don´t think he lost as much as the results suggest. In 2018 he finished 2nd behind Dennis in the long Giro TT. Ahead of Dumoulin and Froome. That´s basically the only long and flat TT we have seen in the last 3 years. He certainly lost his ability to get over smaller hills but when it comes to a high pace on a flat road he is still one of if not the best.Okay, let's not pretend he has the same quality as six years ago.
Last year he never even tried and soft pedaled the TTs in both the Tour and Vuelta.
Most TTs these days are less than 20km long and feature at least 1-2 smaller climbs. At his peak that wouldn´t have mattered but at his current age they are to difficult or short. Even the WCs have been shorter and more difficult in the last few years. Martin won the last flat one in 2016.