[Marcello]

"Some tests have demonstrated that last ATK missiles like russian Kornet are actually overkilling existing tanks since RPG29 are sufficent to pierce actual tanks in their most protected part."

I have my doubts that the RPG-29 can take pierce the front turret of the latest western MBTs. Hull front may be possible (IIRC some time ago a Challenger in Iraq was knocked out by a RPG-29 penetrating the lower hull front), but not turret. Weren't those tests performed on T-80Us and such anyway?
Besides RPGs are relatively short range weapons and the RPG-29/27 and high end RPG-7 rounds are neither that widespread nor cheap.

"I mean, prior to the Strv-122 and Merkava-3, was there anything else to it than thick steel plate, even in tanks of the Leo2/M1A2 generation?"

To counter what threat? The soviets were not awash in top attack weapons AFAIK. They had something but it was not anything worth sacrificing much weight over.

"I think that such top turret add a bit crew survivability versus aerial bomblet, mortar, etc. but not verus top attack atk missiles"

Preventing your tank from being destroyed by a couple of HEAT bomblets with a penetration of maybe 10 cm each seems a good investment today.