They are both unhinged, it doesn't make your suggestion any better lol. Besides, you don't even need their permission, just go ahead, do it, share it on Reddit, and to other raiding discords... Like, you don't need their permission lmao, it's external to the game... The only thing that is going to happen, is most people will think it's weird, at best.
The problem with this, is people cannot use these things responsibly, so it's all well and good coming in with the "But if they allow us to do it..." - Like... People in this community aren't going to use it responsibly and it's only going to encourage further unhinged and cringe behavior... Like the one person that decided to make an Excel sheet which scalped everyone's post on the healer thread, and then linked with FFLogs to create their own scoring system to turn it into a tool of public shaming.. That is the sort of weird behavior you'd be enabling with an inane suggestion like this.
I get it, people lying is not fun, especially when it impacts your own progress or enjoyment, but this ain't the solution to your suggestion, because people absolutely would go beyond using it as a simple list to determine who to blacklist, and I think you also know that lol.
Square Enix aren't protecting anyone, they just apply their ToS, and lethargy is as much against the ToS as any other activity. If you're being banned for "merely letting someone know they aren't performing well", then the chances are you weren't exactly just telling them that their performance is less than what the duty expects. There are far too many people with self-awareness that seemingly doesn't exist, and in many cases where you do actually get more information, it's more often than not that the sanction applied was justified.
There is no big scary boogieman in the team that is secretly out to get those for communicating underperformance, just as there is no big scary boogieman protecting these people that underperform LOL
