Extend Cousins or ... ?

Please don’t give him another extension!   Kirk had only ONE playoff game.   Not worth an investment in him!   Please let him go after next season! 

This is 100% exactly what I think is the right thing to do...

Yeah... if you just want to go by total games played.  

Cousins has already passed Culpepper for 3rd in yards (20,934 - 20,162) and touchdowns (153-135).  He will almost certainly catch Kramer for 2nd on the TD list this year (currently 6 behind) and should catch him for 2nd in yardage barring injury (currently 3,841 behind).  

Or if you're a "results matter" sort of person, you could rank them on win %:
4 - Kramer - 0.454
3 - Culpepper - 0.475
2 - Tarkenton - 0.553
1 - Cousins - 0.581

I think the more interesting chase is actually Cousins vs Tarkenton for the Vikings all time passing marks.  
Yards: Currently 8,323 behind Tarkenton = 4,162 yards / year to catch by end of 2024 - OR-  2,775 yards / year to catch by end of 2025
Touchdowns: Currently 86 behind Tarkenton = 43 TDs / year to catch by end of 2024 - OR - 28.7 TDs / year to catch by end of 2025

You're not wrong that when it's all said and done, Rodgers won't be in any consideration for GOAT and that Brady will be... I respectfully disagree with you about the why though. 

Brady will be considered the GOAT because of the rings on his fingers and only that.  I don't argue that QB play is the biggest factor in scoring points. But it's not the only factor. There are literally tons of factors, and that's the part that people don't seem to get. A good defense is a part of the factor. If you're average starting position is say the 30 yard line instead of the 20, you're going to score more points. If you're defense delivers more 3 and outs, you're going to score more points just as if your offense delivers a lot of 3 and outs, your defense is going to look bad. These all factor into things. Coaching is another big one, and like it or not, if you want to talk GOAT, Brady's coach in NE is definitely one to consider for that title. Personally, I'd arguing coaching is far more important, but that's me.  You excluded Hundly's season in 2017, but oddly enough, you never mentioned Matt Cassel when Brady tore his ACL. The Pats went 10-6 that year and Cassel got flipped for first round pick. Cassel went on to have a great career, am I right?  But that does something, namely that Brady was in a MUCH better system. I'm not saying that Brady was some scrub QB... let me make that clear. He belongs in the hall, but the Brady worship that's going on the NFL has more to do with the rings on his fingers and an overvaluing of his role in getting them. If you don't believe that, look at his 1st Superbowl MVP. He didn't elevate that team. Ty Law won that game with 2 interceptions, one of which was a pick 6. Brady was a game manager at best.  But it does lend credence to Raptorman's point. Tom isn't getting those rings in Detroit, or for that matter, in a lot of places. He probably flames out of the NFL in a few years on most teams... If by some chance his starting QB gets hurt like Bledsoe did, he becomes yet another name of good but not great QBs that never amounted to much on just about any team in the NFL. That says more about the NFL than it does Brady in my opinion, but it also says a lot about how we all continue to over value the contributions of a QB to a game with 11 starters on each side of the ball plus a handful of specialists. 

You forgot to mention one big factor. Brady played twice as long as the other two. But for some, that won't matter.