I suppose you want something akin to this?
It still has its weird spots, most likely because this is just a quick doodle.
The concept/idea is to have smooth, yet billowy terrain. The billows ensure the river must meander in order to find the path of the least resistance, the smooth terrain ensures the pathfinding won’t to the staircasing you see in your example.
Then, afterwards, based on the tributary mask, you must blend the two terrains together using a Cominber[Max]. This automatically creates the floodplains alongside of the river.
Of course, this effect should diver and only be really applied to relative flat areas of your world, as those are the places you expect such meandering rivers.
I hope this helps a bit!
bit-more-meandering-rivers.tmd (133.1 KB)