Difference between Dantooine and Geo Arena. The Arena wasn't an open area for maneuvering and the Jedi were literally under a droid factory pumping out thousands of droids, the novel describing that droids were coming out of everywhere. The Dantooine battle, Windu wasn't underneath an entire factory which was constantly pumping out droids.
Another thing, the droids Mace fought the vast majority of them didn't even fire their blasters, they essentially just stood there with only few of them attacking. Frankly the SBDs just decided to go into melee range of Windu...which makes zero sense given they have blaster arms.
Also forgetting that giant hammer thing that completely wrecked all the clones and droids too, which actually helped out Windu.
The most droids that Windu actually took on at any given time were squads, he never took on the whole bulk of the SBD army, the only time that ever happened was at the very start with the AOE Force attack.
Trying to say that Windu actually took on a whole army is incorrect, he didn't, he took on squads of SBDs, much less thousands and thousands of droids which is what the Geo Arena was about.
https://www.youtube.com/watch?v=cF3ocZu4cZo&t=266s
It's right there.
Count Dooku glanced about the stadium, his smile widening. "It wasn't the Geonosians I was thinking about. How well do you think one Jedi will match up against a thousand battle droids?"
He had timed it perfectly. Just as he finished, a line of battle droids came down the corridor behind Mace Windu, their lasers firing. The Jedi reacted at once, spinning about and flashing his lightsaber to deflect the many bolts, turning them back on his attackers. He knew that these few droids were the least of his troubles, though, for as he glanced around he saw the source of Dooku's confidence thousands of battle droids rolling along every ramp, in the stands and out into the arena below.
- Taken from AOTC Novel
Thousands coming into the arena.