You know where twinned blast is on the tree? What if the ability nodes at the bottom gating the keystones were moved up there over each ability. Then they could be skipped or picked without interfering with anything.
You could take all 3 of them then, but if you went down the middle path and took the ability and it’s 2 modifiers and the keystone and it’s 3 modifiers and then all 3 of the ‘on ability use’ nodes you’d use almost 30 points which seems fair. It’s not impossible to tweak the numbers of those 3 ‘on ability use’ nodes to make it interesting but fair.