Tanks have always co-evolved against their threats. The reason top armor is weak is because the primary threat when the bulk of these designs were originated (60s/70s) was from other tanks or direct-fire guns. Precision indirect fire munitions weren't yet a major threat.
So, when you're rearchitecting a tank today, you're going to protect it against the now-dominant threats.
At its base, a tank is a propulsion system, a gun, and a set of survivability options.
The first two are always going to be relatively expensive, in quantity. So the last gets defined and scaled to meet the expected threat.
I guess you can imagine similar evolution that a century ago drove invention of aircraft carriers. When it became clear that battleships would become too large, too heavy and too expensive to meet their primary goal of dominating the sea around them.
Ie mobile platforms that are essentially defenceless on their own but carry large armament of drones and other electronic devices inside enemy territory that is meant to quickly take over surrounding space (surface and overhead) and do quick job of neutralising various threats like enemy personnel, drones, etc.
But I am not sure about that. Planes require a landing strip to start from and large hangars to store them and that drove the basic form of aircraft carrier.
There is no such limitation for electronic equipment and small drone carriers travelling on land. And I think, rather than presenting a single high value target to the enemy, it makes sense to have a lot of specialised units functioning as one through information systems that cannot be disabled with a single successful strike.
See: GD's TRX concept w/ loitering munitions and a tethered surveillance UAV
> [vs distributed systems]
See: USAF / USN Next Generation Air Dominance programs, or the European Future Combat Air System, which are declared as "systems of systems" to get the desired capabilities. We'll see how far they ultimately lean into distributed though.
So, when you're rearchitecting a tank today, you're going to protect it against the now-dominant threats.
At its base, a tank is a propulsion system, a gun, and a set of survivability options.
The first two are always going to be relatively expensive, in quantity. So the last gets defined and scaled to meet the expected threat.