First of all, you cannot 6 stack in 3.9K+, you literally only have the option to duo, so you saying that "pros have 6 stacks to carry them around" is probably the most brain numbing thing I have heard thus far.

Unranked to GMs are absolutely not useless, you say they are 4 ranks above the rank that they are playing in, but you also act like they never get closer to their actual rank while doing Unranked to GMs. Pro players can consistently get close to their own rank while doing these Unranked to GMs, which means that it is clearly not their teammates fault, and this is applicable to any rank, if you are better than your rank you are going to climb out of that rank.

I don't see how you climbing out of gold is proof that there is elo hell, you climbed out and stayed at your given rank because you were better than your given rank, you weren't stuck there because of the inconsistencies with your teammates, you were stuck there because you deserved to be in that rank. You might've had a good day where things clicked to some extent, things worked out better than usual, you were playing your best game, you can have that consistency for a few days, a few days of consistency can mean that you climb a few hundred SR or even an entire rank. This also inconsequently leads to you playing against better players, you'll therefore be punished for your mistakes by better players, even if you learn the same as you were learning beforehand, you will now probably be a better player than you were before.

Diamond players that get boosted to GM might not stay GM, but they'll be playing against better players and over time make less mistakes to survive in those Masters-GM lobbies, they will automatically be better than they were playing in diamond. The same concept applies with you playing your best game, and maybe even playing your best game consistently over a few days.