French Dunkirk-type ships with British heavy guns

Was France's central shipbuilding weakness its failure to modernize docks and heavy-gun infrastructure?

Yes, and a practical response would be more Dunkerque-sized hulls using British-supplied or licensed heavy guns.

France entered the late 1930s with only two docks capable of building modern full-size battleships, while older infrastructure constrained hull size. Heavy-gun development created another bottleneck and helped drive the compact quadruple-turret solution used to concentrate existing calibers. Building more Dunkerque-style hulls with six British 15- or 16-inch guns would exploit available French strengths instead of waiting for wholly new infrastructure. Britain could supply initial weapons and license later production, potentially giving France three to five powerful ships against Italy at the political price of accepting foreign help.