The moment that wargaming allowed players to be able to switch between ammunition without any penalty is the moment when heavy tanks and their armor became obsolete. It has nothing to do with high tier mediums. If you really want to make armor effective again, fix the changes you made so long ago.
There should a penalty for switching between ammunition. And it should be that you have to reload again to switch to a new shell. Without that, armor becomes useless. As of now, you can go from 200 penetration to 330 penetration in 1 second. No penalty. And yet people still have not noticed this is amazing.