ok in my opinion unreal is going to be better at mobile. Many people says apk sizes are too big and slow on old mobiles. Not fully correct. The trick is finding right settings for your game idea. For example i am working on a runner game has inculuded 4 characters, menus, nearly 20 texture, nearly 15 static mesh etc. Draw calls are 450-500 and tris 250-300k. I get 35-40 fps on my old sony e4g which have mali and 50-55 fps on HTC one and tried on other mobiles which brands i dont remember, fps was fine.
What i do is creating map dynamically in game. if player passed through a door and wont come back, delete door after 2 seconds. Using LOD culling MAX DRAWW DİSTANCE in blueprint -15000 in my case-. Have no light. all materials are unlit. didint use any post proccessing (bloom vs.) Didnt add static meshes directly my map, always used instanced object like actor. Reduced model mesh triangles with blender program. Have played in project settings many times and reduced apk(ETC1) size to 55 mb. i think every game needs different settings. And some mobile devices has old mali GPU like my mobile phone wont render sky correctly.
And note: Physics reducing FPS. For example when your character goes to ragdoll reduces FPS nearly 5 or 10 frame…