Its more that the French guns were quite old and not really designed to punch through something like Krupp's armour. The guns on the
Marceau for example were just a solid iron shell with a slightly hardened cap but otherwise they were quite crude, just a fairly high velocity lump of solid metal. HE Shells had thin shell walls so when they hit and burst it added more to the fragmentation effect. I recall reading somewhere that the RN tried an experiment in the 1900's with a HE shell where its casing was shaped and indented more like a modern grenades to aid with the fragmentation effect, but it just made it inaccurate and was dropped.
A 1904 12 inch gun had a muzzle velocity of 796 meters per second, an older 13.4 did 614 mps. Thats a massive difference when it comes to penetrating armour and the older shell might well shatter when it hits armour it simply was never made to encounter.
The Russian ships were for the most part based on French designs and the French did feature a thin but fairly thick belt with equal armour on the turrets, although the Russians didn't copy the odd hydralic system of how French turrets turned. It was rather unique the turret structure would be lifted off its mounting by about a centermeter by hydralic jacks that were on a rotating base, that then turned and lowered the turret down. It was stable and very chintzy in terms of shiny new tech but vulnerable to battle damage. Most of the Russian ships were a mixbag, the old ones featured older styles of armour but it was usually very thick over the vitals, or the newest ships had brand new Krupps armour but not enough of it. The Borodino's apart from looking very nice and having an awesome name were really bad ships. And I'm glad I helped inspire you Captain Jack!
