Typically, if you're a smurf, you will be placed with those kinds of players. It may be hard for you to notice but Riot's smurf detection is pretty good. ['How come I'm always being placed against Diamonds in my Promos' post by Summoner AverageDong47 here]
Basically, if you have to do any advance techniques and champs or equip summoners like Flash super early into your account and abide to typical strong builds of the meta. You will most certainly be placed in smurf queue.
From any player that has surpassed level 30 expecting to play on a new account it will be almost impossible to see what is in store for a newcomer. Simply because you've already consumed most of the content. If there's one thing that new players will care about, is that content, skins, and gameplay. Normally, PVP games aren't the kind of games you'd want to start a social circle unless you've already built one through a connection of IRL friends or go out of your way to make friends in game. It's highly unlikely you'll want to befriend players in normal matches simply because there isn't much to bond over and that a player's main focus is to win so there's less effort into befriending players to begin with.
It's hard to parse actual criticism of the new player experience simply because a lot of new players are just actually new accounts. I'm sure their first instinct wouldn't be to visit the official forums to write a review of the game. I'm sure they'd visit the r/lol subreddit instead. Even then if they're just getting into the game, they're probably more invested in reading about the game than finding reasons to post complaints about it first hand.
Like, as a new player, there's so much content to look into before you actually visit the boards. Which is literally the end game content where seasoned players will whine about Lux getting another skin, why Ekko is still busted, why mages items are still boring AF, which Vastayan grandpa is going to be their e-sugardaddy, etc. There's literally no incentive for new players to visit the boards to make this kind of comment.
But I could be wrong. I have had my fair share of creating smurf accounts just to sit on cool summoner names and have a 'one-trick' account. Queues are hella long and the players were equally as annoying. So Riot's smurf detection is doing it's job (on fresh accounts).
All I remember when I was genuinely new to the game, the first toxic experience I had was when I was about 22 levels in I had experienced the first time someone intentionally fed as a Teemo.
Plus, those beginner summoner icons, OP. You ain't fooling anyone here.