Not really, it's more things to balance. It doesn't matter you have 20 Runes in one row to choose from If all of them suck because balance team is too busy balancing the 20 Runes of different tree and they don't have enough time.
This is why they also slowed down release of new champs, because there are champs in need of rework who are dead and they wouldn't have enough resources to get to them all in VGUs If they were so focused on new things because "more options is always better". Likewise, having too much Runes (which already counts for 4 new per tree) will just make one extra useless Rune nobody takes anyway, so the graphic interface will show 4 Runes but the player will percieve only 3 like before.
We already have trees where there is this one very niché keystone you barely see taken in some areas. Let's not add oil into fire so quickly.