It's not news to anyone that league has some of the worst grinds to acquire content in any game available. Each level grants you 810 BE, and it takes about 10-15 games to level up (past 30). Each game lasts about 25 min. Even accounting for the average champ maybe being 3150 BE, that's still about 20 hours of gameplay to unlock a single champ.
3,150/810 = 4 levels gained. 4 X 12.5 (medium between 10-15) X 25min per game = 1250 min, or over 20 hours.
(this is excluding possibly unlocking the randomly dropped champs instead of the ones you actually want)
20 hours of gameplay to acquire a middle priced champ is simply ridiculous. I understand Riot wants to make money, and thus motivate you to purchase champs with real money, but come on. There's no excuse for placing champions behind such a huge wall of grind.
Now, to Riot's credit (but also the crux of the problem), they haven't made any champions necessary for success. Meaning, as long as you don't purchase garbage tier champs awaiting reworks, then you have a fairly decent chance to win. **But this is exactly the issue.**
If 141 champions are all nearly equally viable in every circumstance, you simply cannot have a nuanced game of variety. They've intentionally designed them so that they fall into classes that basically do the same thing. Once you have about 20 champs, the only thing left to see is that some of the particles are different on some champs, and to find your preference on which abilities flow together best for you.
Riot is simply unable to create strategy, nuance, and tactical decision making in their champion design and play, because that would create a necessity to own a much larger pool of champions to be effective in the game. **Thus, with each champions release, the game gets more shallow instead of deeper and richer. **
Here's the unpopular opinion that I doubt riot would ever consider, but that would enable them to create much more compelling balance, nuance, gameplay, and strategy:** remove the gate from champion purchase. Allow champions to be acquired much quicker, or make them all playable.** I understand this would necessitate them developing another profit stream to make this work, but I personally believe this is necessary.
TLDR; With all champs being gated so hard, it's simply impossible to balance them in compelling, nuanced, and strategic ways without crippling players unable to purchase a large pool.
**Edit:** Clearly I must've done a poor job at explaining. The problem isn't that it takes too long to get champs. The problem is that because champs are gated, they are designed in a binary way that's very unconducive to real strategic gameplay.
Not sure how to say it any clearer than that...