The console FPS genre is divided into two eras. Before Halo and after Halo. Perfect Dark was good for an N64 game, but Halo changed everything. All console FPS since exist in its shadow and influence.
I can't buy that PD would have served as a killer app for the Gamecube at all, when it probably would have felt like PDZ did: a stale, ugly title better suited for the previous gen.
I feel this view is simply too simplistic. Allow me to explain, and forgive me for partially repeating some earlier posts.
Halo sold 5-6 million copies, and was a huge success. This is well known.
What people keep forgetting for some bizarre reason is that Nightfire was released one year after Halo: Combat Evolved,
and sold 4.9 million copies. (Possibly more, since by some reports it sold 5 million in the first year of release. But there are no reliable sources for that, and no sales figures for the Gearbox PC version, either.)
Eurocom had previously developed The World is Not Enough for N64, a GoldenEye clone that sold a respectable million copies in late 2000. Nightfire drifted from Rareware's design template, but most of the essential elements were intact. Everything from the optional decoupled aiming system -- refined to allow strafing -- to the overall mission design, which while more linear, still preserved a lot of alternate routes and explorable areas and the like. Nightfire was TWINE 2.0, essentially. Complete with TWINE's fetish for bullet ricochet and sexy pistol silencer screwing animations.
Out of the box, Nightfire uses GoldenEye's "left stick turns and moves forward/back" system.
But of course, just like GE/PD, the game has alternate control schemes including a standard dual stick layout. And unlike those games, it asks you to select your preferred layout when you first boot the game.
And it sold ~5 million copies.
A year after Halo had supposedly made this style of game hopelessly "dated".
A GoldenEye/Perfect Dark clone
almost outsold Halo despite being released a year after Halo. One can say, "Well, that's multiplatform dev for you", but the fact remains.