why Legionaries do not loose also cover promotion on upgrade? that unit is clearly OP ........ really guys. Doesn't seems it little unfair to you, that some units do not carry over literally anything? I don't care about their UB/UA is enough to fill that hole after legion. That is unfair and immersion killing for some civs. same for maya. if those units at least going to getone lvl free, it would be somewhat satisfying, but right now, from nice UU, which has pillum and can build roads and forts it is really disgusting and gold wasting upgrade. not to mention, that units like Impi has at least such power, that you have no need to upgrade them into fusilier asap, while legion is a unit for short run.
Also the ability to make UU one era later, while beiing usefull for almost every civ, this is completely useless for Rome.