Heck, in LoL's lore Summoner's weren't ever depicted as being stronger than champions. They just had the ability to summon them, and use summoner spells.
I think it's pretty clear that a Champion is much more powerful than just about any number of Summoners. What we Summoners have going for us is that we have lots of "book-smarts" and more versatile magic. Combat-wise, a Summoner isn't all that impressive, when not being used as intended: to support Champions. A Champion with a Summoner watching their back and channeling more power to them is much more effective than a lone Champion. In terms of stature, rather than raw "power", Champions are heroes and celebrities, and we're their backup. The nicer Champions treat Summoners respectfully; the others are more dismissive. We work for them, not the other way around. In some formal sense, the League favors Summoners, with Champions as guests in our international forum, but in a practical sense they've got more pull back home, where the real power lies. But it's not a competition, Pam! We work together.
The League, all-powerful? Not at all. It's got some power, and a lot of knowledge about magical affairs, but its power lies almost exclusively in the mandate it holds from the nations of Valoran. It's (sometimes grudgingly) respected as the main source of international law in Valoran.
As for why Narrative did this, most likely:
- People like us are not their target audience
- They brought in a bunch of people to "redo the lore", and these outsiders did it in the least Riot way possible
- They want a Runeterran MMO or something, and no longer see making a story for League of Legends as their primary objective
- They're personally ambitious, and like many artists they crave a blank slate and want total control; if they dislike something, they want to be able to obliterate it (which I consider a problematic desire when working on an organic story-verse with an active community)
- They want something that's easy to make toys and other products about
- They're embarrassed by their indie past and are tossing out everything that's kind of quirky or distinctive in favor of industry-standard varnish
It's also entirely possible that they just screwed up. It's hard to imagine Riot hiring a team like that, but maybe they really did just fail to seriously try to understand the League and Summoners. Maybe they really didn't know that there was an active lore community in the path of their bulldozer.
I don't think it's malice. I think it's just them not caring about us. We're super-hardcore lore people, and we'll keep doing our League of Legends lore, even if it means diverging from their Leagueless League lore in a few places. We're already invested.