This map sustain with 4 socketed voidstones can't be intended.

This is still happening for me, I got around 100 burial grounds map when it was favourited using 2 Voidstones, when I got 4/4 void stones I switched to Crimson Temple (now t16 ofc) and I got ONE in 30-40 maps.
Switched back to Burial Grounds with 2 Voidstones and double drop on one of the first maps i ran after changing back!
Please look into this GGG, using 4 Voidstone is objectively much worse for my map sustain.

Edit: After switching I had all favourite slots unlocked except 2.