I've seen what a Hasselbeck-less and Wilson-less Seahawks team looks like.
I also have seen what happens when you tie your boat to QBs like Stafford, Carr, Schuab, Dalton, Romo, Prescott, Goff, Smith, <Insert Browns QB>, Bortles, etc.
Paying a QB is not a total detriment to a team's superbowl chances. While Tom Brady is taking a less contract, he's still made it to 3 of the past 4 Superbowls.
Matt Ryan made it to a Superbowl. Manning made it to 3 Superbowls being a highly cap-restrictive position. For every Rookie Joe Flacco, Ben Roethelisberger, Russell Wilson or Collin Kaepernick, there are guys like Cam Newton, Eli Manning, Aaron Rodgers, Drew Brees and Kurt Warners.
In the past 8 SBs, only 4 QBs have shown up for the AFC and 7 in the NFC; AFC P Manning (2), Tom Brady (4), Ben Roethlisberg (1) & Joe Flacco (1) vs NFC Aaron Rodgers (1), Eli Manning (1), Colin Kaepernick (1), Russell Wilson (2), Cam Newton (1), Matt Ryan (1) & Nick Foles (1).
The biggest thing is investing in the right players; whether that's the QB, DE, OL or P. The NFL as a whole does not define what is best for the Seahawks given they are the only team to rush more than they pass, the only team to have 2,000+ yards rushing and how lost 5+ Pro-Bowlers from their defensive roster from last year.
I have yet to see how Wilson's current contract prevented them from retaining any of their best players. The best player they lost was due to betting on the wrong player and that was Percy Harvin over Golden Tate. There's no other former Seahawks who was released or lost in Free Agency that has gone on to have a better career.
Here's the thing, no franchise will willingly give up on their QB. The fact that Kirk Cousins can get $84M guaranteed is less about Kirk Cousins and more about how much the position is coveted. If anything, it proves that Washington was right for stringing him along for as long as they could. They are not that far off from where Minnesota is right now but they lost their QB so they are shot.
Russell's succcess is so hard to replicate and I feel that we (collective "we") too often look at the fantasy numbers to justify who is good/bad. Lamar Jackson is on a great tear right now... but Russell has been Russell for 7+ years now. There's no sign that he's holding this team back in any capacity and that is valuable in-of-itself.
The other issue is that there is not always money to spend on these great talents in Free Agency. The best bargains for Seattle have been guys that no one wanted (Arvil, Bennnett, Baldwin, Browner, McDaniels, McDougald, etc.) or were willing to give them top-dollar so they took a short-term deal to try it out.