The system is just objectively better. Now the difference between two players of equal skill isn't who has T2 vs T3 runes, because everyone has the same access to the same shit and it comes down to player skill.
Also, you got robbed of nothing. How long did you utilize the old rune system when you put money into it? You paid for a product and used it, and likely had a considerable advantage over PLENTY of others (many like myself only had T2 runes, and that was once the 1IP sale became a thing) for a decent amount of time.
You CAN STILL CHANGE YOUR RUNES dependent on who you're playing against. I don't see how you CAN'T do that now. The option wasn't taken from you - if anything, now there's quite a bit more variety than just flat stats. For example: Sion won't want comet against someone like Cho in lane because the poke now means nothing, so you can take other keystones like Grasp/Glacial Augment.