Actually I've poured more money into this game than I care to admit. Not only have i perpetually owned every champion for years, there was a point I had at least 1 skin for every champion as well. So please don't assume something if you don't know it to be accurate information. I most certainly do own every champ.
Champions are always available to play for free, nullifying your argument that they're required. All champions aren't required to play, just one is, and there's 15 (used to be 10) every week.
You made the decision to invest money into unlocking champions instantly. It doesn't matter how much easier it is now than it was before, you got what you paid for, which at the time was grind free, wait free champions. Nothing about that specific part of the system had changed.
Champion shards of course don't feel useful to anyone with all the champions, but Riot isn't obligated to give out free loot in the first place, and trying to satisfy everyone is unrealistic. The goal of the system is to make newer players feel rewarded for their continued play.
For other people that don't have use for champion shards, you can disenchant them for blue essence, which will be used at later levels to unlock level exclusive rewards, such as icons, emotes, and the like.