One of the weapons that threaten our M-1 Abrams is the top-attack anti-tank missile. Armor on the top of tanks is much thinner than on the front or even the sides.
Active defenses that would shoot down these missiles (and any other missiles) are being developed.
But why can't we use methods that have worked to protect our light armor with thin armor on the front and sides from standard anti-tank weapons? My worry about the Stryker in combat was highlighted by the fact that the Army did not send the vehicle into combat as is. We put metal cages around the vehicle to detonate incoming infantry-fired HEAT rounds to disrupt the molten stream that would burn through the thin armor had it hit the armored hull directly. It worked.
Could we mount a similar (and cheap) slat armor on the top of the turret and over the rear engine compartment to block top-attack warheads? Could reactive armor panels facing up also work?
I don't think heavy armor is obsolete. But weapons are out there that can kill them.