I think the summary of many players’ grievances about the new matchmaking system is that visible rank is not reflective of hidden MMR. It may seem petty to some but the little symbol that shows others your “skill” is a source of pride for many that play the game. There really is no reason that these things should be different from one another by any significant margin. I understand that Riot is trying to make changes so that individuals can catch their visible rank up to their MMR but I think that at no point should they be different. If Riot wanted to reset visible ranks and cap at platinum 3, then they should also have set the MMR of radiants who maxed at plat 3 at whatever MMR value would correspond to that.
Players do want to have fair and balanced games that are challenging. But that needs to come with an immediate reflection of their skill in their visible rank I believe, because that visible rank matters to many players. I get that Riot thinks that this may encourage more players to play more often to “grind” for rank, but it is quite honestly frustrating and is probably has the opposite effect.