Based on your own charts, if you adjust it to the bare minimum FC level which is 6, then adjust to only leaders with a lvl of at least 90 and take away all crafting classes that leaves us with a very different story. Spriggan is the number one shell FC producer with 395, followed by Kujata (130), Excalibur (125), Zeromus(115), and Louisoux(112). Japan is not the #1 producer of Shell FC's it seems to be Europe, based on the top 5 and the numbers alone. If we extend it to top 10, we include Chocobo, Midgardsormr, Twintania, Omega, and Typhon. Again Europe seems to be in the lead.

For funsies I lowered the leaders level to 50 and only allowed for the 6 starting classes to be used, which is almost a guaranteed way to tell if a FC is a shell or not. Gladiator, Pugilist, Conjurer, Maruader, Lancer, and Thaumaturge. Spriggan again is number 1 with a staggering 319, Kujata (88), Excalibur Loisoux, and Midgardsormr tied (75). Top 5 still Europe. With NA in second. Lets extend this to the top 10. Omega(74), Chocobo(71), Typhon(67), Ragnarok and Twintania tied (55). Looking like Europe with a strong lead so far. Based on top 10 Europe with a solid lead, Japan is second and NA is third.

I could go on, also by default Japan has more servers, so by default they probably do in fact have more shell fc's but I didn't bother to count past the top 10.