I feel like FSJ is strong just because it has no major weaknesses, and the typical airborne weakness of armor doesn't exist with the combination of the high-vet popguns and the Hs 129. I'll complain about the popguns endlessly during a match, but immunity to light armor and armor within 600m isn't a bad identity for a division that's focused on phase A dominance. The Henschel on the other hand has no vet but has crazy resilience, surprisingly good accuracy, and is really easy to keep alive with a high-vet fighter screen; just fly in a couple fighters to take flak, have the Henschel pop a high-value target of your choice, then evacuate everything. It shores up another weakness (9+ armor at max range) and makes the optimal way to fight them just shoving recon and artillery down their throats behind an AA screen which is boring (especially as the french no Im not bitter about all my stuarts dying shut up)
If, statistically, they are too good, I think toning back down the base Henschel would be the way to go, and buff up the Henschels of other divisions to compensate.