To be honest you probably learn more faster with those Diamond and plat players than you do getting pooled with new players.
After a couple hundreds of games, you might find that you sped up so much that they aren't near as intimidating, and you're a lot more reactive to team demands.
I can tell you this much: If you try to enter ranked, you will probably land in silver, and you will learn nothing from them, because they are just as if not more so toxic, and will directly try to sabotage your play. You'll spend so much time fighting verbally that you don't have the brain processing left to realize the imperfections of actions, gear choices, team countering, winning against a counter, etc. Every game will instead be a lottery.
I'd play with those Plats and Diamonds as much as you can. Just tell them at the beginning that you are unranked and learning and ask for tips. MOST of them will try to play around that in norms. You might get up to a high Gold level of play there without playing thousands of ranked games and ruining your chance to climb.
If you instead play your thousands of games THERE, you can probably carry yourself in ranked to Gold + in less than 50 games. If you try to Learn in Ranked, expect 1600 games + to still be Silver, or worse. Bronze.
P.S. Some Diamonds/Plats will coach players if you befriend them.