To be fair League of Legends has a really fair system in this regard and considering the context of how League got made I feel it should get a pass to a certain degree.
When League first got made it was a handful of ex Dota All Stars staff who decided to make the game. They didn't have gigantic amounts of capital to fund the game and kick starter didn't exist at the time. With this in mind they basically only had a really good idea that they could sale.
So that's what they did they sold the idea and the company to Tencent to get the game going. This is a stark contrast to Dota 2's development which had all of Steam as a platform as both it's capital and as it's marketing platform (Being the first listed F2P game on Steam for years has a huge marketing value).
Thus why 1 game needed a revenue system that looks greedy and why the other can give every hero for free.
Anyway with the context of the how and why lets look at the actual systems they employ.
Currently there are 4 ways to get a champion.
Purchase it directly with Riot Points (purchased currency). Someone can also gift you the champion through various means.
Purchase it directly with Blue Essence (Earned currency through games played or dismantled items).
Earn it through a Loot box the game gives you on level up.
Earn it through a Loot box you earn through you or someone on your team getting Mastery Rank S on a champion in the game.
The reason I think it's rather fair is because now with the new BE and Loot box system you actually earn free champions at an extremely fast pace, in fact much faster than ever before. In addition to that if you get champions you don't want you can dismantle them to get BE (on top of the BE the box already gave) so you can purchase another champion.
This with the added benefit of Runes being repurposed and given for free means the only real BE sinks in the game are champions or optional cosmetic items like Emotes. Furthermore the boxes can also give you things that can only be earned with RP such as Skins of any quality (even the most expensive).
All in all I think for a game that had to sell it's soul to the devil to get made (Tencent) it actually has an incredibly fair system and gives you a ton of options on how to acquire content you want. In the end the loot boxes were just added on top of systems in place already as a means to just get extra free stuff , rather then remove systems in place to force you into buying more stuff.
I'd say thats probably why you don't see much issue with Leagues system, it's actually not predatory due to all the systems around it.
Now if they had extremely reduced the amount of bE you get, and increased the amount of time it takes to get a level up. Or left Boxes as purchasable only instead of giving you the option to earn it as well as buy it. Then yeah it would be shitty