In the modern era -- where practically every weapon is designed to kill the MBT -- tanks need to grow much larger or much smaller.

LARGER:
> Much thicker armor that can't be penetrated by conventional AT weapons.
> More room for anti-drone and anti-missile systems, e.g. CIWS, flak, etc.
> Stronger EW suite.
> More room for ordnance, munitions, and supplies. Can be used as a mobile depot for infantry, reducing reliance on those poor trucks that keep getting blown up.
> Much more redundancy. Multiple tracks, multiple compartments, multiple guns.
> Much better crew survivability.

smaller:
> Faster
> Cheaper
> Quiet variants can be run on battery power. (I know, I know. It's situational.)
> A more natural extension of the role of infantry
> Unmanned or single-manned. If it gets popped, it's not a disaster, build three more.
> Harder to see, harder to target, harder to hit.
> Swarm tactics.

That the German military is buying 2000 MBTs is the height of retardation. Wordwide military leadership, having taken orders all of their lives, is incapable of innovative or critical thinking. You could put Patrick S. Tomlinson or Chris-Chan in charge of the German military and they'd probably do a better job, lol.