I disagree, in the 80s it was often about leaders fighting it out at the head of the race, for which the truly strong guys could mitigate eventual losses in TTT. By contrast, these days the high budget teams attempt, and often succeed, in controlling the race and sending even GC guys out the back in the process. Now give such team/s a longish TTT at the beginning of a GT and it's all but over from the start.I think having a TTT while making it essentially mean nothing in GC is a terrible idea. The best part of the TTT is it forces teams to pick one or two rouleur/TT types that they otherwise wouldn't have picked, and therefore being weaker in mountainous terrain, making the race potentially harder to control in the mountains.
Im a bit torn, as I heavily dislike very short TTT's and think they are a meme and useless for the race, but on the other hand don't like plus 40-50 TTT as the advantage is simply to great for the big teams ON TOP OFF already being better off riding for those teams in the other stages. Its quite a conundrum to me, so I guess a TTT around 20-30 km is fine in that it keeps time gaps in check while it still means something.