Grand Offensive is a powerful commander that is perfectly in the middle ground in terms of popularity (and strength). The Panzer Commander slot helps balance out the commander that has 4 other very strong abilities, and it's a nice upgrade for P4s (arty) or Panthers (sight and accuracy) anyway.
And I don't see how changing Panzer Commander for a 105mm barrage offmap would have made Grand Offensive OP
Regarding the sight bonus, Grand Offensive is the doctrine with Panzerfusiliers, the infantry unit with extra sight range AND flare, and the heavy tank means it will only be used at best on one vehicle unless you don't use the Command Tiger
This way of "balancing out" is exactly my issue with how WFA commanders have been designed, a rule that doesn't apply to EFA. Purposefully stuffing together in the same commander (actually it wasn't on purpose btw, Panzer Commander was meant to be used with Tiger before the due nerf) abilities that don't work well together is a questionable design choice that just makes commanders bland choices between 3 or less actual slots.
What's exactly meant to "balance out" in EFA top picks like Spearhead Doctrine or the new Soviet Shock Army? Nothing, all slots are equally important and great useful abilities.
EFA commanders are balanced by making the commander lack in 1 or 2 aspects, be an off map, an elite infantry, an heavy tank, recon, a good loiter... This is a sensible way of balancing
WFA commanders are "balanced" by wasting a slot on an ability that will most likely never ever be used or having 2 slots that lack synergy. Would Sector Assault be OP in Grand Offensive? Yes. Would 105mm barrage be OP in Grand Offensive? Most likely not, and would fit better a doctrine that already has recon options and the only OKW tank that can't use Panzer Commander. Probably it wouldn't even change the pickrate of the doctrine one bit. It's no "major" change.
Airborne is a powerful commander that is top 3 in terms of popularity across all modes. It has a powerful offmap and the team weapon drops are still way more efficient than backteching.
But at the cost of TWO slots, one necessarily being useless as you'll tech for one or the other. EFA gets a bundle drop. It's a doctrine without any special armor or artillery option that competes with Urban Assault and Tactical Support.
I also generally disagree with the notion that used = "good" or used = "doesn't need changes at all". Have the Tigers commaders ever stop being relevant picks if not top dogs of OST commander meta before the Tiger buff (and it was considerably buffed)? If the Tiger commanders were already popular does that mean that the Tiger buff was unnecessary?
Feuersturm is ridiculously strong on city maps and top 4 most popular commander in teamgames.
It's a commander with lots of abilities for bonus dps against garrisons and cover and the total OKW commanders are 9, meaning it's slightly above average in teamgames.
At least to me it doesn't seem remarkable at all and I don't see how being the 4th best out of 9 doctrines means it should have an almost wasted slot