Well so basically you're saying the Unreal engine can in fact create a battle royale game that runs with good performance as its been done with Fortnite Battleground (runs at 60fps and looks better to boot), so why is PUBG so broken, unless you're claiming epic has purposely cripple PUBG somehow? I think its more just the team and not the engine per se, just look at all the aspects of it, not just the performance. eg the animations of the ppl are just laughable, the textures etc
Fortnite is 30fps, the map is smaller and the world is a lot less complex.