In a properly balanced game, this should also apply to Runes. If the champion requires a specific rune set to be viable, they should be altered to make other options plausible. By that I mean if the Riven player falls behind in her lane because "lol i got aftershock instead of electrocute", then it's probably a good sign that the Runes provide too much influence over how the champion can be played.
Playstyle and champion diversity is nonexistent right now. Wasn't that the main focus of Runes Reforged? To make it so I could choose between several different nuances to either best fit my own tempo or to overcome my shortcomings? I understand that no matter what, there are always going to be keystones better for certain champions than others. Hecarim will always get better use out of Predator than Xerath will. But abuse is rampant, and the "optimal path" is pretty standardized for every champion regardless of their lane and your confidence in besting your opponent. Not having the right runes means you can't best your opponent. The Runes should not make the champion, the player should.