From what I've read so far the book by Jordan and Dumas does not really answer the question of whether the slow rof of the Riehelieu was ever improved. It gives the rof of Dunkerque as 1.5 to 2 rpm, a bit below average but not serious, although they had excessive dispersion problems too. The electic power output of the Richelieu was higher than that in the Bismarck, so lack of power would not seem to be the problem.
The dispersion arose from the insertion of a 40 mm splinter bulkhead in the turrets, as a means of mitigating the excessive concentration of armament in the two turrets, and resultant close pairing of guns. The quads in the KGV class had no bulkhead, a uniform and larger gun spacing and no dispersion problem. Rate of fire was 2 rpm, I believe, although they did have more problems than other turrets and mountings, especially compared with the twin 15 in. Other ships, e.g., Bismarck could fire salvos in different modes, e.g. alternating fore and aft turrets (which was preferred) or one gun in each turret.
The problem with rof may have arisen from overcomplication. My impression from the above book is that the French favoured complication, unlike the British who preferred simplicity. An example are the French shells with dye bags and detonators for these in the nose, and canisters for poison gas in the base. The latter were the cause of shells exploding in the barrels at Dakar. If they'd kept them simpler they might have been better.