My input to when I was new.
To me. What is a terrible experience to new players is that there's no real explaination of how to really play league. The importance of certain items if you playing a particular champ, (runes and masteries) I think runes reforged will fixed this issue a bit.
I found this game long when it was in beta I believe. I counldn't play it then because my computer at time was like a rock not even a toaster. I was running vista with 512mb ram xD.
I really got into the game when I got a new PC and someone I met in another game told me they played it. I was like okay, my PC should be able to handle league now and with someone who is used to it. It be a good experience for me.
At that time, I understand nothing about ADC's, mages, assasins and anything of the likes. My friend tried to explain it to me but I still really understand much of it. I just play a champs I like and bought them when I get IP, I even spent RP on a few (when they discounts) and the starter pack bundle. I'll just buy runes and put them in. Masteries, I sorta pick whatever.
In my early games, I had bots but not has much has now. Although, I once played a game where I think I was the only actual player (it was an ARAM).
Learning to play this game, I practically figure a lot on my own. A few people help me along the way. Then I don't think the game was toxic has now when I think about it. Since every now and then I meet toxic ppl in AI and even ARAM.
New players will enter this game with little to no guidance of champs and their roles. No idea what runes or masteries to take on particular champ. When to buy certain items and not always follow RIOT's recommendations. They will buy a champ maybe because they like the look or the gameplay with no idea how play that champ properly. They will know not the importance of warding, and last hitting. They be ignorant of many aspects of this game. And one day will play pvp and get seriously flame for this lack of knowledge. I have seen it and experience it. For this many will lose interest. Learning league takes a lot of time and it can be dishearten if there's no one to help with the process. In the end, the ones who will continue will be those who really like what the game has to offer itself. I liked the champions(not all some I regret purchasing xD), I enjoy learning how to play them, some are exciting to play some are not. For those who stick to games because of the community, they likely not to stick around.
A way around this maybe to implement a Mentor and Apprencticeship. Both parties have to register for it. An evaluation will be done at the end. So for those who really want to learn this game can and those who wish for others to learn can teach. or A very informative and detail tutorial should be made.