I did a count today just for the gold and rainbow girls that are not max level yet.
25 Gold, ranging from lvl 1 to Evolved lvl 60.
4 Rainbows ranging from lvl 35 (Sakura) to Evolved lvl 60 (Black Baccara)

Black Baccara leveling is on hold, since I removed her from my teams (She could replace Camellia in Team 2, but I like Camellia's art much better, not to mention that Camellia is way faster)
Fritillaria lvl 51. But she's on an ATK Ampy / Skill Bloom diet for now, so leveling is.. slow.
Anemone is Evolved lvl 38 now and is on priority for yellow manyus, since I already installed her in the Counter squad.
Sakura is currently getting purple manyus, but I'm not in a hurry until we get bloomed forms. So should I get a more interesting magic type, then she'll be placed on hold.

Of my 4*, only three reached Evolved lvl 60 so far. The rest are in various states of undress leveling, few are actually evolved.
Of my 3*, only Sasanqua reached Evolved lvl 60. The rest, again, are in various states of leveling and evolving.
Of my 2*, none reached evolved lvl 60, the highest is Amaryllis at evolved lvl 31.

I'm not sure I'd want events to be put on hold to give us time to level them though. I actually doubt it'd help in any way.
I think I'd rather see the 2* girls dropping from the 80-stam event maps replaced with lvl 5 manyus or something like that. I don't have a problem with too many girls, but rather with too few manyus.
Even the Seed gacha is a pretty terrible source of manyus.

I experimented a bit with playing a lot of Seed Gacha, and merging the lvl1 2* girls into a lvl1 3* girl, resulting in a lvl 9 3*, but that lvl9 3* gives about as much experience as using a lvl5 manyu of the wrong color, so it's not extremely helpful, and rather elaborate. Hence, bringing actual lvl 5 manyus into the drops rotation of 2* girls for high stamina maps would be way more effective.