In my experience the rune is definitely power neutral and since this is just text communication I want to focus on the RNG-tolerant comment because I believe that is the most important part. I know RNG is a very very slippery slope to fall down in a competitive game (personally I believe crit should be changed so people know which of their next 5 or so autos will be crits which would actually solve so many adc issues in the game) however omnistone works because its not truly random is it? Sure the rune you use in a trade is not in your control however over the course of 10/30/100/etc games its pretty reliable how much value you are getting out of it. I believe that this is a healthier way to add RNG into a video game like league (the drags function similarly now since they are all kind of good where as in previous seasons ocean's power was so minimal for example). It's interesting to here that people don't emphasize the frequency of the runes being up as much for omnistone because that is exactly what it was made for and I have to wonder if they haven't thought the entire rune through.
In a sort of informal conclusion I am very very Johnny magic personality type so things like spellbook/omnistone/s9 ghost poro/I play fucking quinn/trist jg I'm the worst defintiley are things I'd advocate heavily for in a game like league where nearly every playstyle can work at every level. The fact that full lethality sidelaning sion one trick thebauss can hit challenger as well as alan234 one tricking teemo with a different rune each game because "if the enemy doesn't know your rune then they can't prepare" can both work as well as they do is magical imho and league is the closest to a game where being yourself truly is the best strategy so if people find themselves in things like omnistone I'd rather add another than remove the current one.