Well of course! If you push specular IBL contribution to the extreme and isolate just that contribution, of course you should get falloff on the grazing angles. That’s the fresnel effect!
The point of the glossy fresnel compensation (which Unreal certainly implements, but maybe in some simplified way, otherwise the results would be very different) is just to reduce amount of fresnel effect based on roughness, not remove it all together. You are complaining about seeing fresnel. It almost sounds like you are proposing to remove fresnel altogether and have just constant reflection regardless of angle.
If you crank up IBL specular contribution and isolate it to see the fresnel effects, then that’s good that you see it. It means it exists. If you saw just a flat sphere, that would be a lot more concerning.