I can give the martial arts prowess part (the longer the Dragon Ball series goes on, the worse they get at that compared to their roots, which I miss very much) but I don't think blurr lines are necessarily complicated and detailed movements. It's rather stiff in comparison. The organization of three (honestly four counting the parts with 17 and his ki blasts swirling around the pair, hitting on point to the musical beat) characters, two working in tandem took a lot more thought and care.
I still stand by my opinion that as far as general animation goes, that fight between Goku and Cell is pretty standard, though higher up for Z just from being able to see what's going on in many points.
The blur lines parts are what give the sense of speed, combined with how fast the environment is moving. The DBS fight looks slow by comparison. The general acrobatics are just far more prevalent and detailed in the animation from a technical perspective than just flying at each other like a kid smashing his action figures together.
Time to get autistic, bear with me.
For example, look at Goku dodge Cell early on. He jumps back and uses his hand to flip off the ground at 0:10, from an animation standpoint it adds to the sense of agility. 1:37-1:58 is a great sequence of dodging and countering by Goku, you can
feel him trying not fall off the edge with those nimble movements and getting back on his footing as Cell hunts him down. Toward the end of that sequence they both go tumbling in a really easy to follow shot, something the Super fight struggles with (for example you never see 17 land from his dodge from Jiren's attack).
That type of weighty animation lends the fight a more visceral sense to it, check out this knee by Goku at 1:14. Super feels like it has no gravity, which is ironic considering ToP had 10x gravity and flying was disabled, whereas Cell's fight is just on regular old Earth and flying is allowed.
Look at the Jiren fight in comparison, the cinematography is much less clean. The very first clash is obscured and ambiguous, dust covering the impact, which basically sets the tone for the majority of the fight. The cleanest strike is landed at 0:41 and doesn't feel like it has much impact, compare it to the aforementioned Goku knee. After that is the volley of invisible strikes Jiren uses, cool but suspiciously convenient for the animators.
When Frieza tackles Jiren it's again just a dust cloud on impact. This kind of thing really is lazy and the effect the lack of contact has on how the attack feels is hard to ignore. It happens a THIRD time during Goku's badass save, you just see dust and debris at 1:28. The most powerful looking attack is Jiren slamming Frieza through the ground at 1:22, but much like in the aftermath of Frieza's tackle the camera isn't following the action too well, we could've seen a better angle (the initial portion is great, but half the shot before the closeup to Frieza's face is obscured by a rock at the low angle).
Keep in mind some of this is nitpicking, but in terms of just sheer visual spectacle the Cell fight is more clear, 80% of the character movements aren't relegated to flying at each other or shooting beams or having convenient visual obstructions (which is cool, but more actual articulation in the combat maneuvers would help with variety).
