Hmm is that really true?

I guess the real question is "Why does the 13.5" quads and level 71 duals outrange the
strasbugged and richelieu guns?"

To be fair, US BBs have the same issue. The shells fired by the 16" Mk 2 and 3 guns
(Colorado, Tenn 45, SoDak) hit ~10% harder at max angle than those of the 16" Mk 7 (Iowa).
And the 16" Mk 6 guns (NoCar) hit substantially harder.

How the ships compare in other factors (eg: speed, range, AA, scouts, turning force) also
matters, and may be sufficient.

Where are you getting your numbers?

If you're going by the numbers displayed ingame under the gun/ammo stat, don't.
Those have never been accurate and never will be accurate.