[Lucid:]

I like your list Hermes. According to that, I am part of these groups.
Non-ranked: .1% people just there for rank practice OR if playing with friends, 7% trolls, but that's mostly in a good/friendly way like "We should play an all assassin team!" or "Let's go all mid!"
Ranked: .2% Bad players that are friendly yes, but should not be in ranked and .1% Nice people who will fill and are actually communicative and useful (I don't believe these two groups are mutually exclusive.)

When I was around level 15 or so, Lulu came out and I decided I needed to play her. I would duo with my roommate at the time who mostly played AD Carry. I had a blast playing as support and bought even more support characters and eventually came to "main" support. I'm definitely a lot better at squishy mage/utility supports than I am with tank supports, but that's okay because nobody complains if someone is willing to play support, ward, and not take their creeps. It sounds like you really like jungling so I would suggest doing something similar. Buy as many junglers as you think are interesting and focus on learning that role inside and out. Watch pro matches to see how the pro junglers play and see what the strengths and weaknesses of each champ are. Everyone loves somebody who knows how to jungle well, and if you're good enough at it, you can win games by winning every lane for your team.
(TLDR; What Law said.)

In ranked, if you main top/mid you need to know how to play other roles well, but if you main jungle/support you can almost always have it. I have played top probably twice ever because people almost always call top/mid, and my husband plays top in our team of friends so I have put almost no effort into learning top. I can handle it if I need to, having a few bruisers that I play in 3v3, but I don't know the matchups well and I tend to play too passive. I have never lost as Zyra mid in ranked, but I've only had 4 games with her as mid. I play her support enough to keep my skills up. I only know how to jungle Shyvanna and, as of this last week, Cho'gath, but I rarely need to jungle either.