Ammo Shell and Damage Parts

What’s the point having different shell when shooting open top tank with AP and HE Shell have simillar damage and also in website it says the damage will be base on parts what i shoot, so i thought it will be more like war thunder instead of wot but turns out it’s not, saying shoot base of parts and have hp at the same time doesn’t make sense to me how you gonna make this work ? why not just make it like war thunder. War thunder also have arcade battle but without health bar since you guys planning to make realistic mode in future without health bar