In patch 5.3, three major skills were re-balanced: Expert Marksman, Basic Firing Training, and Advanced Firing Training. After 5.3, they mainly affect main guns of up to 139mm, which covers all destroyer guns and just a handful of cruiser guns. Secondary batteries, of course, aren’t affected at all by the size limitations.
The question is, why 139mm specifically? This restriction excludes a few cruiser guns, namely those on low-tier Japanese cruisers – so, hardly a serious balance concern, as I don’t see people complaining about Yubari being too overpowered because of her guns.
Right now, the largest gun on any destroyer in-game is the Russian 130mm, well under the 139mm limit. When the Russian destroyers were introduced, one of their selling points was that they had the biggest guns, bigger than anything mounted on Japanese or American destroyers. It just so happens, actually, that there’s another set of destroyers with guns even larger than those of the Russians – guns that fit just under the 139mm upper limit for the three aforementioned skills.
For the French Navy, 130mm was, in fact, small. They developed the 138.6mm/50 gun – with successive 1927, 1929, and 1934 models – for use on their destroyers, which sparked a sort of destroyer arms race with Italy. The guns on French destroyers ended up becoming so big and so numerous that destroyers such as Le Fantasque were occasionally considered light cruisers. Le Fantasque herself is likely the most famous of them all, managing to reach a top speed of 45 knots, blowing away her Russian counterparts in yet another category.
In my opinion, the changes to EM, BFT, and AFT were made explicitly with French destroyers in mind, destroyers like Mogador, Le Fantasque, and Aigle.
It’s inevitable that the French Navy, the Marine Nationale, will be added to World of Warships. I wouldn’t be surprised at all if they arrived early next year, alongside their natural rivals the Italians, with a cruiser branch: French destroyers and Italian cruisers, similar to how Russian destroyers and German cruisers were added in autumn.
Then again, the devs have mentioned that they have four planned branches arriving this year, and of those, only three are accounted for: German battleships, British cruisers, and Russian cruisers. Could the French, perhaps, be the fourth?
We’ll have to wait and see, unfortunately. Without a doubt, though, I’m sure I’d fall in love with the French destroyers, and I hope they come soon.
Sources: en.wikipedia.org, http://www.navweaps.org