You wouldn't expect to win a card tournament with a starter deck

So don't go into Ranked with the expectation that you can be successful without knowledge. There are plenty of laning, mechanic, and teamfight tutorial videos that provide information that is absolutely necessary yet not provided by the game's tutorial.

Some information that you need is basic to the lane you're trying to play. That info would be like staple cards. It's like energy cards in Pokemon, land cards in Magic, or the extra deck in yugioh (unless you use monarchs, last I checked). If you don't have those, you only stand a chance if the enemy is equally lacking. But the information-- or those cards-- is not hard to find.

And that alone can get you decently far with many champions. The characters in this game are generally not designed to be incredibly difficult. Slightly more in depth knowledge of laning can get you ahead with easy, rarely changed characters like Darius, Annie, Vayne, or Leona.

But a few characters have drastically high skill caps, such as Azir, Taliyah, or Aurelion Sol. And their effectiveness mirrors the effectiveness of having someone else build you a good deck of cards. At first, you'll make more mistakes than with the simpler champions-- you won't see exactly how the cards work together. And you'll actually lose more even if the champion/deck is stronger. Then, when the champion-- the deck-- becomes second nature you'll see an incredible increase in your effectiveness. So there are in depth tutorials for more difficult champions as well.

It is your due diligence to do the research if you think you're ready for ranked. The game's tutorial gives you next to nothing, unfortunately. But the massive community has been doing their part to help. Just go to youtube. However, this is where the most important difference between readiness in a card game and readiness in this game comes in: you aren't playing this game for yourself alone. If you lose tournament after tournament because you don't have a single Mystical Space Typhoon, it's on you alone. No one else is effected by your ignorance. But if you continuously lose matches in Ranked because you don't know how to handle Rumble's overheat passive or how to farm while avoiding poke, you're a detriment to 4 other players as well.

So don't play ranked if you aren't ready. People are there to play the game seriously, with others who put in the necessary preparations in order to win games. It's a detriment to your allies, and it doesn't help you improve if your only wins are against players who were so far below your team that they could lose when you're unprepared. There's a mode for casual players, and it's where you belong until you're ready.

[EDIT] This is for the benefit of both the player and their allies. There's no reason to play ranked if you'll be placed in bronze and stay in bronze due to your own ignorance anyway. You don't gain anything from it but frustration. And there is nothing you can learn from playing bronze ranked that you couldn't learn from norms. You have to go out of your way to research tips and tricks because Riot's tutorials are completely inadequate.

If I had it my way, bronze wouldn't exist. Players bad enough to be in bronze would simply not be given a rank and given a time period before they could try again.