The Trips theory is that the system is an intentional paywall to get people to pull/buy shards out of frustration, which is a pretty crappy way to treat your players.
I don't think Tag rank should be a barometer of "worthiness" to earn a champion. If a player can do every other mission in that chain, they've put in their time and effort. Some of the missions are pure cheese, but others do take some time, luck and effort. The difference is that they CAN be done without having six teams of meta Arena champs.
The player power creep makes Tag rank a moving goal post that effectively shuts out new entries to the gold ranks. If someone can get into G1 but gets demoted the next reset, odds are pretty good they will either advance again or stay in the S4 slot. For example, I've been in S4 solidly for months because I don't have enough of the meta champs to advance to G1 (I don't care how many times someone says "Git Gud" - if you don't have the same champs you see over and over again you AREN'T making the cut). So I'm effectively holding an S4 slot. If I drop to S3, the odds are good that I will make S4 again the next week. So good luck trying to get into S4, which is 100 times easier than S4 to G1.
The G1 mission is effectively backlogged. So unless they open those brackets considerably or implement a handicap system, the REAL number of people that can advance is effectively MUCH smaller than the already ridiculously low number of available advancement slots listed.
Some people are even changing their account names to some variation of G1 mission in hopes that people will have mercy on them - which probably does them more harm than good in that effort.
I expect the player outcry on this to increase as more people get stuck on that mission. Maybe Plarium will do something about it eventually, but they should have already if they actually pay attention.