Well since your referencing me i might as well reply to this to help to shed some light on how climbing the leaderboard works for soloQ and what to expect.
To begin SoloQ your limited 50-100 and if you go past 50 you could bounce out 15 spots with just one loss. But staying in top 50 means 1 of 3 things:
1- Youre really really good and consistent, but only like 8 players are currently able to do this.
2- You are quitting the game so you dont take losses against groups and go on an "artificial" win streak (99% of people do this and if you do it you should be banned)
3- You are somehow avoiding backfills because they do affect your rank despite it not effecting your win rate.
Now to address your comment on rank decay. There is rank decay and a lot of it already. if i dont play the game for 1 day then i drop roughly 4 spots regardless of a win (from ranked #1)). Another thing that makes you lose rank even if you win is if you dont actually win the game fast enough vs low ranked players.The next thing that causes a drop in rank is if the lobby never started. That counts as a quit and it drops your rank a 0.5 spots noramlly (So two of those in a row is a loss in rank). Finally, 1 real loss is normally 8-10 spots down
I think what you actually want is to have live ranked decay. As of right now i dont have to play the game again and my account will stay at the same ranking unless someone passes me or someone drops below me. I too agree that live ranked decay should be a thing, that way you know if you should play a game or not to keep your ranked spot. However, that will not stop people from have 3+ accounts in top 10. Why? because they simply play more than you. They have enough time to play multiple games on multiple accounts.
Now to answer the follow up question you have that might be... "Gunked how do you climb so fast with fresh accounts in order to have them at that ranked?"
The simple answer is... dont lose. The top 7 people all play exclusively together because the skill gap is so large between them and everyone else. If any 4 of those 7 people play together then they wont lose to any group or combination of players that currently plays the game. For some reason that group is called "The Illuminati" which is a weird story and im not a fan of it.
So if you wanna climb soloQ to the #1 spot just never lose
Edit: Forgot to talk about your idea of soloQ leaderboard only. I also agree that if there was a ranked mode to queue into then it would have to be soloQ only. Anything more would be unfair. However this leaderboard isnt a traditional ranked leaderboard and it instead goes off "trueskill" so dont take it so serious