Not a single Z plan ship was somehow overarmed or out of (very moderate) German design practices/philosophy. If anything, they're on the opposite side, over engineered for what they were bringing to action.
Wiki, citing Garzke and Dulin: "Hitler demanded guns larger than any possible adversary, but guns of the caliber demanded by Hitler would have required displacements of over 80,000 long tons (81,000 t) and drafts so deep that it prevented the use of Germany's ports without significant dredging. Fuchs eventually convinced Hitler that the 40.6 cm gun was the optimal choice for the H-39 design"
The Z Plan was ridiculous over-reach, consistently demanding performance that would have challenged the best British or American designers.
6x H-39 BB: 53,300t, 30kts, 19,000nmi @ 19kts, 12x diesel
3x O Class BC: 28,900t, 35ts, 14,000nmi @ 19kts, 1x steam + 8x diesel
12x P Class CA/ACR: 22,145t, 33kts, 25,000nmi @ 13kts, 12x diesel
6x M Class CL: 9,300t, 36kts, 12,000nmi @ 19kts, 2x steam+ 4x diesel
6* x Spahkreuzer DD/CL: 5,700t, 36 kts, 7000nmi @ 17kts, 2x diesel
All displacements standard.
For comparison:
Iowa: 48,110t, 33kts, 14,890nmi @ 15kts, 4x steam
KGV: 36,727t, 28kts, 6,000nmi @ 14kts, 4x steam
And then there's the design escalation of H-39 (4x2x406mm/16"):
H-41: 4x2x420mm/16.5", 68,800t, 28.8kts, 20,000nmi @19kts
H-42: 4x2x480mm/18.9", 90,000t, 31.9kts, 20,000nmi @19kts
H-43: 4x2x480mm/18.9", 111,000t, 36.7kts, 20,000nmi @19kts
H-44: 4x2x508mm/20", 131,000t, 28.8kts, 20,000nmi @19kts