Even GX had rubberbanding as it's a good way to artificially increase difficulty without making complex AI.
If with rubberbanding, we are talking about the CPUs "teleporting" from one part of the track to another (without actually driving that section), it didn't exist in GX.
Most people probably thought that it did exist ("teleporting") because the CPUs drove better than most people

If a player read the game manual and then played GX, the CPUs would still know more about the handling system than the player. The CPUs would use more effective turns.
The statement "the CPUs didn't cheat in GX" is more true than not. So they did cheat then!! yes, in story mode.
Story mode was a little mode with only 9 missions. In some of those missions, some CPUs would have higher stats that they were supposed to (including more than the regular 100 enegy points, meaning that they could boost more than the player). This was noticeable mainly in two missions: chapter 2 and the infamous chapter 7.
In chapter 2, fire stingray (your rival's ship) had better stats, including 10.000 energy points!! instead of 100. He would boost or not depending on what you did, so you could still beat him as long as you didn't try to out-boot him from the very begining.
In chapter 7, your main rivals also had better than normal stats. Bood hawk had 150 enegy and black bull 180 enegy. The point of this mission was to kill Black Bull (which started right behing you) at the begining of the race.
You could get angry at this and say that it's unfair, but, if you think about it, your rivals are not skipping some sections of the track. They are there, taking every corner, as you do, and you can beat them.
Anyway, most of GX's content (ships and tracks) was in another mode: grand prix. In grand prix, the other 29 ships didn't have better stats than you. In fact, it could be argued that they had worse stats than you, as they all used 50% accel/max speed settings while you could use 100% max speed.
Did the CPUs, in grand prix, go faster when they were behind? actually, yes, a little bit, but they never got close to the lap times that the player could potentially get, doing the same things as them, but better. Even without custom ships, and without the use of techniques that the CPUs didn't use, you could be unreachable for them. Even in master class, driving better, your lead would increase little by little, until it was massive.
I can only think about one exception: Phantom road. In that track, there's a point near the end of each lap, where the CPUs will chain a couple of boosts, fly of the track for a moment, and come back right before the finish line. Because of that sequence, they will get ridiculous fast times there. Phantom road is also a great example of the CPUs turning more with just the analog stick than what is possible. They have an easy time in a circuit that is a nightmare for the regular player.
All i'm saying is that, even though the GX CPUs will react better to some situations that what you possibly can, or even though there will be some sections of the track were they go faster than you, they won't be "teleporting" around the track.