Black and White isn't paced well, it's just back-loaded. Those two aren't the same.
Don't get me wrong, the finale of Black and White where Team Plasma takes over the Pokemon league is the best in the entire series. And I think having that occur at the end of the game instead of between gyms 7 and 8 isn't a bad thing.
But ending on a high note while having a mediocre middle isn't the pinnacle of good pacing. And Black and White really did need something to spice up the middle. Compare the Rocket Game Corner, the Lake of Rage team-up with Lance, or especially Po Town from the Sun and Moon games. A big interesting dungeon where you face off against either the main villain or a sub-villain, a "rising action set-piece" to boil the tension. But that doesn't ever happen in Black and White, all the big stuff goes down at the Pokemon League.
I guess that Dragon Spiral Tower was supposed to be that set-piece, as N claiming a legendary Pokemon could have been a real moment in the plot. But they flubbed the execution, as N takes off immediately on dragon-back and you're left with just some common grunts (the same ones you've been fighting all game).
Black and While really could have used some sub-villains to fill out the center, because fighting grunts and occasionally N felt really same-y after a while. And what bothers my mind is that Team Plasma had a gigantic cast of character but they barely used any of them! The Shadow Triad, the sages, Anthea and Concordia, so many characters yet none of them really do anything. The sequel solved this, but in Black and White fighting grunts all the time just lacked teeth.
And despite moving the showdown with Plasma to the end of the game, it still doesn't solve the Gym 8 slow-ride. Just instead of breathing easier because the villain plot is over, now you're just wondering where did the plot go. As again, N jets off and Team Plasma disappears without a peep until the surprise at the Pokemon League, so there's no sense of urgency in the plot. It doesn't feel like a threat, just that something's missing.
In short the pacing of Black and White isn't a 45 degree ramp but a flat plane with a gigantic spike at the very end. And yes, that finale was really something, but I can't call this "good pacing" to have the game so back-loaded.