Fully enhanced Lunera is incredible, just used one as a friend on JP. She had around 600SPR only but it was enough to heal 2k HP/120MP every turn on top of the 90% buff.
It seems that the healing output is similar to JP enhancements; the big difference is the 40% vs 90% stat buff. I have to wonder what GL's Lunera +2 enhancement is going to be since we already got the +1 enhancement.
It seems to be the healing output is relative to the max HP and MP of unit.
Conspiracy theory :
Gumi is adding 2 units to the Nier event because they know 9S TM is too good, and adding another 4* unit would make people having to pull more to get him.
I would hate if they added two 5* units like they do in JP.