I've no real problem with the rebirth concept itself, just the way Lunia handled it. (As well as myth being separate)
Rebirth should be something only preformed when you've hit the maximum point, in this regard being level 90-99 with every 2 additional levels being the +1 SP and level 99 being the final 2 addition (being 5 total)
The person is then torn between using rebirth and losing the level 90+ for bonus stats, or remaining as is.
As it stands, rebirth happens at level 70, which is easy to get too, reaching level 80-90 when you're above 6 rebirth is a joke.
That's what made it more redundant for me, was just the ease and the choice was a no-brainer, you rebirth the moment you hit the monthly timeline.
Though I can already hear the screams of "oh my god that would take forever to grind"; but that's the point.
Torn between two decisions.
Wings and the level circle would actually have meaning that way; you'd actually be "pro" for having wings and getting 3 damn rebirths to do it.
Myth has to go..