Saying that soloQ showed your rank compared to others is wrong. Explain how playing in a team game with 4 other people shows how good you are by yourself. A group game cannot truly rank how good on person is unless that person is stomping. Even in that realm you have to factor in all the variables. Get fed off your lane opponent on an OP champ and carry the game? How is that about your individual skill. You are basing your ego off of what happened against one person who may or may not play that lane regularly. The game is about communication and yes there can be times when a pre-made doesn't communicate well just like a random group of individuals. Same goes for how a random group of individuals can click and shit stomp the other team. What's different than before. Play a support style champ win lane and have your team feed or have bad positioning can cost a game the same as getting paired with a toxic pre-made. Oh you got camped by a jungler / top duo what's different than solo Q that existed as well.
I say that people are upset because they have constructed this belief that what they did in the solo lane, only a fraction of what the game is about, is equal to their true skill level at the game. Instead of viewing this as a waste of time (fyi that puts you on permanent tilt) look for ways to bridge the gap. I play solo, with a friend or in a group of 3 or 4 sometimes. It all depends. I win more games solo than I do with friends, but one thing I rarely ever do is rage. I play, I do my best sometimes that's not game winning. Sometimes I carry sometimes I get carried and provide support to my team. At the end of the day my goal is to win and that requires communication and fighting through the toxicness that comes from players thinking they are better than they are. Trying to lead without being a jackass. Making suggestions over demands, but too often in SoloQ I have seen the same toxic nature that I read on these boards about DQ. Players take the team game and try to make it about themselves and their accomplishments. At the end of the day the ranks are not important and it really is about your own personal ego. You want to feel important and special in this game, but you can do that just by playing your best.
You can say that makes me casual or not a hardcore player, but when I have time I spam games like anyone else. I'll play for 8 hours to 10 hours straight in soloq mode. I want to win I want my rank to go up, but it does't always have to be about me getting a quad kill in a game. I care about making the play that wins the game not the play that I can touch myself over.
The claim that ranked integrity going down is unprovable outside of your anecdotal evidence. Even that shows contradictions. Posts about pre-mades dominating followed by pre-mades losing terribly and raging at the solo q player. If in your mind you could carry a group of randoms past another group of randoms than it should be no different in a pre-made, but then team play enters the field. No different than in solo Q when a champ got fed and you focused that one player hard and shut them out later in the game.
I understand that you feel slighted. That your gaming experience, which is so tied to your ego is being damaged. That is not riots problem. WoW went through much the same things when arenas were introduced and cross realm pvp was introduced. Everyone said it would destroy the game that people would not stand for it yet the game is still going strong today because someone will play. Maybe not you maybe not the other elitest who think they are actually doing something with their lives through this game, but people will play. I see so many posts here about having problems on smurf accounts, which is the real cancer for any game. Ruining the experience of new players does not increase the number of players. How many potential good players stopped before they started because they could not even grasp the game because 2 seconds in a smurf slapped them silly. If you play a smurf you are part of the problem. Not only for new players, but for ruining the lower ranked tiers. Going into a game either demanding respect and trolling when you are not given it or stomping the poor bronze player forced to deal with you ruins that levels ranks. That might have been a win for that player, but they had the odds stacked against them because of your smurf. Where's the difference between that and "omg they are premade". Boosting existed before DQ and ruined the experience for those dealing with it.
TLDR: grow up I don't care what your rank is. There is no competitive rank until you hit a point where you are competing for something other than your ego stroke.