I'd prefer a standardization to 2 UUs and one UB per civ, it could alleviate some balance issues.
Germany and Japan could get industrial or scientific buildings to make them less overspecialized for warfare, England could use a good economic building to make them less useless. The Vanilla Enhanced Mod for example makes the Ship of the Line a generic unit available for all civs and gives England a windmill UB with +1

and +1

on tiles with luxury resources.
I agree, I think this would work well to balance civs out. For Siam, they should add the Yantric Cloth Bandit, or Bang Rajan Warrior, man those guys were tough! It could be a replace for either pike or musketmen.
Yes, and they were right to make SOTL available to everyone thats how it should be, don't they have a historical advisor at Firaxis? If not they need one badly! Give the Brits a damn redcoat for crying out loud. Give the US some Marines, or Airborne Rangers, something to toughen them up like they should be. Navy Seals perhaps, thats an idea! They should give the Russians a shock army.
"The 'Shock' armies were created with the specific structure to engage and destroy significant enemy forces, and were reinforced with more armoured and artillery assets than other combined arms armies. Where necessary the Shock armies were reinforced with mechanised, tank and cavalry formations and units. During the Second World War some Shock armies included armoured trains and air-sled equipped units."
Maybe this could be associated with a UB of some type. Or it simply could be represented by a different tank, Katyusha rocket launcher, or Soviet style WWII artillery piece, that represents shock army. Maybe they can only be built if a city has a UB for building Shock armies. The UB could be a Military District Headquarters, or some viable name.
There are so many things that could be done to improve the game. What it will take is imagination and balance playtesting. This game could be 100 times better than it is currently. And I am not saying it is bad at this point, but the diplomacy needs to be tweaked somewhat, along with improvements to the AI.