is it basically an improved version of h1z1?
Not really, what people need to understand that the gamemodes used in BR-mods for ARMA II/III, ARK and H1Z1 was made by the guy that goes by the name of PLAYERUNKNOWN (he even worked on H1Z1)
Battlegrounds is far more immersive and fun compared to the goofy style of H1Z1 that has retarded carmechanics and animations and Battlegrounds uses the ARMA III-engine.
And in Battlegrounds you also have the option to customize weapons with different styles of gadgets that will enchance the weapon. Armour and Gear also comes in LVL1/2/3 etc. Jumping out of a moving vehicle will instantly kill you in solo-rounds and get you downed in duo/squad.
The game is far more realistic then the broken microtransaction H1Z1 will ever be.