IMO arty was the natural enemy of TDs. And it is working like in nature. You wipe out the predator, another comes up to take his place.
Again IMO arty was nerfed too hard. It needed a nerf and it is good that nerf happened but I think it basically made it extinct and even if its present you do not need to fear it so much. I could probably count on my one hand times I was one shooted by arty after the nerf or on count on two hands I was seriously damaged by it. As a consequence TDs came out from their holes and took up an empty space in the food chain of tanks.
I do not have a problem personally with TDs, some are harder to counter than others but this is still normal and in reasonable numbers 2-3 per game (I am still talking about high tier games) they are not a problem. But due to not having a natural enemy their numbers are increasing and that becomes at least in my eyes a problem, cause 5-8 TDs per side with the amount of alpha they can pump out means they can one shot (2 TDs shooting at the same time) you pretty much anywhere (slight exaggeration) on the map while you need few well aimed shots due to most having a good armour.
I knew that the whiners will come after TDs as soon as I heard about the arty nerf, but nerfing them is not a solution, because then they will move to whine about heavies, then about meds and so on until we will be left with nothing more than bicycles and sticks to put them in the wheels. For me the solution will be to slightly buff the arty, mind you very slightly, only to the level where TDs start to be afraid again to stand in the open in packs. That's my personal opinion on that matter.