The developers don't care about if this is realistic (no ship design was changed fudamentally in any way but the technologies I listed above was as important as the change to deadnoughts). Like they don't care about if you can build a battleship in half a year is unrealistic.
What they care about is making a good strategy game.
Well there's a helluva big difference between the air tenders of ww1 and the fleet carriers of ww2 and the same can be said of some destroyer-classes and subs as well.
The difference between a Colorado and a Bismarck is almost down to experience spent on ticks on the Variants in comparison.
Radar, rangefinding, shells and other technological changes, even increased bore and and elevation of the main guns were brought up to speed on a number of major surface combatants prior to or during WW2 without building completely new ships. The differences in battleships or other heavy surface combatants weren't all that great as to justify special care.
The higher reliability base of a "modern" battleship will make Bismarck less susceptible to critical hits compared to an older one like HMS Hood. The higher speed of the Bismarck compared to a Colorado will make a world of difference on the strategically noticeable scale. And so forth.
All in all I'm pretty happy with what we've been shown so far (with the exception of fuel but that's discussion not suitable here).