I completely came into this thread expecting that it was a thread asking for an IP sink due to the massive excess amounts of IP some players accumulate, and was going to point out that it's tricky to balance 'worthwhile' ip sinks and also allowing new-ish players to be competitive.
As it is though, the subtle differences in raw stats is going to be negligible compared to the skill differences that players while accumulate over the course of earning the ip for the runes/runepages/champs. Also, I very much disagree with the assessment of 70% of the game being IP grinding. At most it's 70% of the level 1-30 grind, and I think the process of leveling an account to 30 is a pretty small portion of ones overall league "life" (which has all of ranked and LP grinding ahead of it once it reaches 30).
Over the course of 1-30, you're still learning the fundamentals of the game, and playing random free week champs and focusing on learning game mechanics is the most important thing. By the time you're 30, you have enough IP for a couple full runepages worth of runes along with a handful of champions you really enjoy, and you can go quite far just using those. (A generic AD page and a generic AP page will pretty much cover you for the majority of champs.)
The only time that you really might benefit from that micromanagment of rune pages is once you're at the upper tiers of ranked play, and you'll have 100's if not 1000's of ranked games under your belt by that point, giving you more than enough IP to cover all your needs. Prior to that, the minor differences in stats really won't make nearly as much difference as your raw skill. It's easy to fall into the trap of thinking "No fair you had better runes than me!" rather than "No fair, you were a better player than me!", but really in the vast majority of case, it's the latter statement that is relevant, and if you focus on improving your ability as a player, you'll get an excess of IP falling into your lap at the same time without even thinking about it.
Now it's true that it's frustrating for players who already know what they're doing (e.g. smurf accounts) but they're sortof an edge case not necessarily worth actively supporting even if they're not condemned, and occasionally you'll try a new free week champ and discover you really want it but don't have the IP, but that's part of why champions are buyable with RP too.
