Another bad reply i will give like always.
i think i have fallen in the dark side of the force

Try BV engine : when editing a terrain you can add as many textures as you want
and edit the terrain with them (paint, choose x,y UV scale etc ..)
each time this is a one more render pass , that's to you to not use too many.
It could be cool if 3DGS in the future could also manage automatically any number of textures, but for 5 i find it's really enought
