I think the first thing you have to accept, in any ranked, is that there will be smurfs, afk's, toxic teammates, tilted teammates, etc. The thing about that is you are the constant factor in all of your ranked matches. I understand people are frustrated, and like to assume that someone who is destroying in their match is a smurf, but realistically they aren't as common as I think the community believes. So no matter what, yes you will have games with smurfs or AFK's, but realistically you should play enough matches where those matches are a small factor in your overall ranked history.
Before I burn myself, we have AFK penalties incoming. We are definitely aware how awful having an AFK teammate is in ranked.
To answer your first question, all the players in your match are of the same skill(or atleast the match maker thinks so). So you really shouldn't be playing actual immortals in silver, unless that immortal player is being tested(has their MMR) at silver. This is how you also prevent players from getting carried or boosted into higher ranks. You can have a 5 stack carry a player all the way to immortal from silver(it would be extremely difficult the ranked rating gains would work against them), but if that carried player never raised their skill MMR they will still just be silver. They will get matched against silvers, play like a silver, gain nearly nothing for a win, but lose a ton for a loss. The system will push them to silver, and they won't ruin immortal level players matches because the match maker is making them play against players it believes is at their skill. If you think of the system more as testing you at a rank, then pushing you to that rank, that's exactly what it is doing. The nice thing is that the system keeps players where it thinks they belong in skill, and while you are progressing in rank it corrects until you converge with your MMR.
No matter what, you can't stop it, your Rank and MMR will converge. You play placements, the system says "Hmm I think this player is gold" then you get placed probably in low gold or silver. If you keep performing well in your gold level matches, you will keep getting more Ranked Rating per win, and less per a loss, until you are gold. If you start to underperform, the system will drop and say "Opps I was wrong, this is a silver player" and after a few matches you will be at whatever silver tier you are suppose to be at. It usually takes 20-30 games tops to converge with your MMR.
So in a sense, during your first 20-30 games your forward facing rank is probably wrong. But that's true about any ranked system you play in. No ranked system you ever play in will give you, or know your true rank in your first few matches(even after placements). In fact the Elo system used in chess takes 1000's of matches to determine true rank, and that's for a game that doesn't have changing rules like we do(new maps and characters). So you could argue ranks are never correct, and you are never at your actual rank until you've played 1000's of matches. If we wanted to go really far down the rabbit hole, technically every video game ranked system you play defines who is what rank. For example, we decide how many players to let into Radiant, what MMR you need to be immortal, what MMR is diamond, etc. That's how we ensure that "Top 2% of all players are X rank". Because we know, generally, where the MMR of the entire player population sits. We could say 50% of the player base is now diamond, etc. Someone, in every game you play, is deciding what your MMR means as a rank.
I think there is a big misunderstanding, or at least there is a perception the system is broken, when people are silver and see a diamond rank in their lobby. That player may have a different forward facing rank, but they are just on their journey to find their true rank. If you are a silver player, with Plat MMR, and you get paired against plat players then those plat players are at their MMR(but you aren't). So you are a silver player, tested to be a plat, and to join the ranks of players that have already converged at their rank. Those plat players are trying to get better, because the only way they will climb is by winning more then they lose in the plat skill level games they are playing in. The system cares about putting you in fair matches, to test you. It also creates the best competitive environment, because we don't put you in artificial matches that are made just for you to grind them. If we made you grind through all the ranks it's meaningless if you aren't playing matches that are testing your actual skill.
Whew that was super long. Thanks for reading! I love talking about these things, and it's a very confusing topic so let me know if I didn't explain it correctly. Also thanks for engaging with me on the topic, learning how people think about this(that aren't like me and work on it all day all the time) helps a ton. Gotta keep making the system better!