Looks like the wider community is not too fond of the grind either. We are 3 days from the end of the event and not even half-way to getting to the 10 trillion points required for the maximum gold bonus.
Yeah, I don't have all that much experience with the higher level content yet, but hitting them as often and as hard as you can seems like a way forward. For now, I got a foot in the door, but both Sage Laeva and the Scene 3 Mother still trounce my current teams with ease and they bring up some really big guns after a certain number of turns, so it looks very much like a damage race. The best I've been able to do is to bring Mother nearly down to half health with the help of some negate and a few lucky breaks.
I've also looked at Streptocarpus and Royal Water Lily, cause the wiki talked about them under Prison Mother and Sage Laeva, but damage buffs seem to be better for this role. Also, Hydrangea does have the advantage of being easier to get. Any direction I go seems to require a lot of rainbow medals and they don't exactly grow on trees.