It will actually be very easy, like you said, on certain maps/situations don't lt there be tanks, there are many stages of the big battles where tanks were used, and in small skirmished give japan the ability to use recon planes and China not to, Japan will be the attacking forces so I Don't see the harm on giving tem a sub par advantage.
And yes while not every platoon didnt have marksmen, most of them still did.
want to know what won't be easy? balancing out a far inferior Japanese force equipped with a decent bolt action and a lousy sub machinegun vs WW2's best semi autos and the Thompson/BAR
Defender's advantage doesn't apply when the defender simply lacks weapons physically capable of denting the attacker... Even in 1944, Japanese armored forces consisting mainly of obsolete Type 95 and Type 95 tanks still managed to erase the territorial gains the Chinese had made over the past three years in a single offensive. I don't think you're understanding the point I'm trying to make here, but the Chinese would have no artillery support, no tank support, no recon, no HMGs, no smoke grenades, one LMG, and no anti-tank weapons! I mean, even giving the average Chinese rifleman two grenades would be stretching realism already. And I'd hate to see what their unlock tree would look like...
And I don't know what sources you have at your disposal, but most Chinese conscripts not belonging to elite divisions never fired their weapons in basic training and were terrible shots. Add that to the COMPLETE and TOTAL lack of scoped rifles, even Lend-lease, in the Chinese arsenal, and the idea of marksmen in most platoons is laughable.
It's a good thing nutrition, morale bordering on mutiny, linguistic miscommunications, supply difficulties, lackadaisical training, poor command structure, lack of even basic medical facilities, and chronic mistrust between officers and men wouldn't make it into the scope of an MP FPS, because those factors were an even greater reason behind the historical imbalance.
Like I said, certain maps would work. The defense of the Sihang warehouse, for example, or the Battle of Pingxingguan--both of which give the Chinese a decisive terrain advantage.
A couple of NRA vs IJA maps bundled together with US vs Japan themed Rising Storm would be excellent. People would play those maps as something new, a novelty item. It'd be a great idea.
An entire 64-person multiplayer game? Six to eight multiplayer maps? That would be difficult.
Just imagine: want to level up the MG class? Best to play as a Japanese. Want to level up the commander class? You'll get those arty kills as a Japanese. Tank? Japanese. If the current ruckus over the Panzer IV's dominance weren't enough, imagine the rage of players on the Chinese team, a Type 97 on the hill above their spawn virtually invincible as it destroys everyone from spawn. And if the RS team were dedicated to historical accuracy, the Japanese would have the option of mustard gas as support.
It'd just be an awesome deal playing as a Japanese! No need to worry about arty, snipers, or tanks...
Balancing them against the Americans is much simpler. The Americans have a small arms advantage, but the Japanese at least have the LMGs, HMGs, terrain, and support necessary to give them a real defender's advantage on the late-war maps where the Americans have better support. And even on those late war maps, the Japanese will still have access to artillery support, called in via radio. Tanks, while outnumbered and obsolete, were at least available to them. And even if not, their 37mm and 47mm anti-tank guns were actually surprisingly effective against Allied armor from ambush positions in the close-quarters environment of Pacific Islands. Add high morale, an iron-rigid command structure, generally well-equipped soldiers, and a few truly effective weapons like the Type 99 LMG, the knee mortar, and the Type 99 rifle, and it's a far more even fight.
And before anybody mentions German equipment purchased before the war or Lend-lease weaponry shipped to China, most of the former was lost during the early battles in 1936 for Northern China and Shanghai, and the goliath's share of the latter was saved to equip Chiang's best divisions--which were held in reserve almost throughout the ENTIRE war in preparation for the inevitable civil war with the CCP.