If a metaphor is allowed:
Unity might be like the Ford Taurus of game engines. Well known (at least in the US,) reasonable second hand value, easy to find a mechanic when it breaks.
Unreal might be like the Lamborghini of game engines. Very fast, very sexy, but breaks more and harder to fix when it does.
Now, is the argument that a Taurus is the right car for everyone? I think that would be a dumb argument. Different people prefer different cars. Different developers need different engines.
And, honestly, I feel Unreal Engine 4 is more like a BMW – maybe less reliable than a Toyota Camry, but not at the trouble level of the Italian supercars. For that, you need the pre-release UE5 download 