Unsure about Festung Support, I mean it's ok in it's current state imo. I always end up failing to activate Relief Infantry ("dam, lost tons of infantry, should have had it on..."), but it's rather a l2p issue for me I guess.
The mortar ht is a must have in the doctrine imo, I mean it sets up faster, more durable in mortar duels and those flame shells come handy at locking a vp.
If any change has to be done about the commander, then I say it should be the addition of some sort of recon option to spot for the mortars and artillery.
As for Luftwaffe Supply doctrine, the fuel/muni drop should stay, it's one of the doctrine's major selling point even now (seen a video, where this ability was used to summon a KT for an OKW player at 15 mins). Another thing I'm unsure about is whether the Luftwaffe field officer should have the recon call on him or the incendiary bombing. I mean any ability on the officer would have limited range obviously, but would be cheaper too. Personally I would prefer Recon staying as a commander slot ability, so it could be used anywhere on the map, in conjunction with the 50 kg bomb.
On the OKW Fortification doctrine I don't think ostruppen are necessary. The commander is mainly used in larger team games, where ostruppen dont give much advantage over volks. Also they are called Osttruppen for a reason.
Maybe Volkssturm, but again, not necessary imo.