Strongest starting unit
That should probably go to brits, because they start with a mainline infantry. Sturmpioneers are way weaker than people think they are and lose most engagements unless they ambush the enemy at closer range.
Infantry that doesn't require to research weapons/nades (gets them from basic teching)
Axis get those for "free" because the buildings and overall tech is slightly more expensive. OKW also starts with the least amount of fuel.
Being able to upgrade some infantry weapons in hostile territory
They were designed to be an offensive faction, this comes from that design just the same way as paratroopers or stormtruppen are able to upgrade behind enemy lines.
Infantry not dropping AI weapons on low models/wipes
That's not exactly a bad thing, imagine volks dropping their STG's next to Obersoldaten, I don't think anyone would want to deal with that, and no one would exchange their bars/brens/dps for volk STG.
Unique vet system
It's 3 vet levels spread over 5 vet levels.
Most secure base structure defense that negates light vehicle base-rush
Because they have no (reliable)counters for an early light vehicle. Without those AA guns in the base, game would be over for OKW the second M3A1 comes out.
T0 raketen and AT options for almost all infantry later on (shrecks, fausts)
Raketen is pretty much the worst AT gun that relies on cheesy mechanics. Every faction has a snare and shrecks are stuck on an engineer unit that's expensive to maintain.
KT without using up a commander slot and no way to deny it by destroying the tech structures
And Brits have a Churchill which is much more cost effective. KT is basically free vet for enemy TD's and AT guns.
Elite infantry (obers) without using up a commander slot
They die easily to light vehicles, can't deal well with vetted up infantry without vetting up first themselves.
Overwatch doctrine with double abilities
You can't judge a faction because of one doctrine that's overpowered, + USF has those too.
Free AA building with teching that outranges infantry vision
It's also easy to destroy, and it's vision doesn't outrange all infantry vision either.
Is there an aspect where they get the short end of the stick?
With strong generalist and specialist tanks and probably the best mobile artillery in the game they seem like a very low risk high reward faction.
My guess is that some of the things were balanced around not having a sniper (although having the option of one of the best anti sniper units in the form of JLI) but once snipers have been nerfed this faction was never adjusted.
Well, they do get the short end of the stick in non-vehicle AT department. The generalist is the most expensive non-doc generalist in the game so it probably should be better than the rest of them, STUKA is predictable and not exactly the best mobile arty(might be the best rocket arty but that's debatable). About JLI, when the snipers were "nerfed", they weren't that strong at all, they were only in scavenge doctrine and were pertty mediocre tbh. I don't deny that OKW probably is the strongest faction but it's not because of the reasons that you think they are. It's all because of one stupid doctrine + more or less overperforming mainline infantry, take those two away and they'll probably end up going from top tier to bottom tier.