We've seen a single Jedi destroy a nice amount of droids alone and here (at 1:30) we see just 2 Jedi and one padawan (and two clones) hold off a nice amount of droids, so how did any Jedi die on Geonosis? There were around 202 Jedi vs an army of droids but proportionally the Jedi should have easily swept the army. Instead, an estimated 179 died. That seems pretty ridiculous considering there were a large amount of Jedi masters at the battle.
Any thoughts?
According to Dooku, the Jedi were outnumbered by a thousand battle droids to each Jedi. There's really no good reason to assume that he was exaggerating.
“I don’t think so,” Mace countered. “The Geonosians aren’t warriors. One Jedi has to be worth a hundred Geonosians.”
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?”
Ultimately the odds mounted up, and although each Jedi gave a good account of themselves, ultimately the droids and Geonosians only needed to be lucky once.
But despite all the gallant efforts, despite the mounds of slaughtered enemies, Geonosian and droid alike, the outcome was beginning to show clearly, as the Jedi were being pushed back by sheer numbers. The general retreat flowed toward the arena, though that area would provide little respite. In addition to the droids and Jedi, the two monsters rushed about crazily, destroying everything in their path.
The film's junior novelisation is even more blunt about the cause of the Jedi's failure
The fight was the worst Obi-Wan had ever been through. It was far worse than Naboo had been. The Battle Droids kept coming and coming, endlessly. No matter how many they destroyed, there were always more. At one point, he found himself back-to-back with Mace Windu. They seemed to be making progress — and then Jango Fett rocketed down to join the fight. Mace went after the bounty hunter, and Obi-Wan was on his own again.
There are too many of them! Obi-Wan lost count of the droids he had destroyed. He could feel Jedi dying around him, overwhelmed by sheer numbers. The sand of the arena was soaked with blood and littered with droid parts, and more Battle Droids were still coming. The three execution-monsters were dead — Obi-Wan vaguely remembered killing the acklay himself — but that hardly seemed to matter.
The Star Wars in 100 Scenes factbook puts it very nicely.
Not even the Force can overcome hopeless odds.
In addition to being outnumbered, trapped, and in an open space where they don't work best....
All Lightsaber forms are not created equal
While it is true that we see the protagonists of our story wrecking loads of droids left and right throughout the trilogy, it must be noted that they were masters of lightsaber forms that favored combat against blaster fire. Obi-Wan Kenobi relied on Form III, Soresu and Anakin Skywalker relied on Form V, Djem So. Most other forms of lightsaber combat were not so dedicated against blaster fire as these two, and instead were oriented more towards dueling.
Also of note that the Battle of Geonosis marks the first time in several generations that the Jedi entered a major conflict, thus forms dedicated against blaster fire were not as necessary and likely less popular among the Jedi.
Finally, it is important to note that our protagonists are some of the most powerful Jedi in the original trilogy, especially Anakin Skywalker, known as "The Chosen One". Where other Jedi would go down like fleas, they prevail.
The other answers focus on the strengths/weaknesses of the Jedi themselves, and the overwhelming odds against them. I just want to point out that aside from being outmanned/outgunned, the Jedi were also hopelessly outmaneuvered.
Their predicament reminds me of the Battle of Agincourt, in which a superior force of Frenchmen were defeated by the tired and hungry Englishmen. You can read the Wikipedia article for a full description of the battle, but I believe there were a few reasons for the French defeat:
1 - They did not use their long-range assets.
"They had plenty of archers and crossbowmen but nobody wanted to let them fire [sic]. The reason for this was that the site was so narrow that there was only enough room for the men-at-arms." A different source says that the French did not even deploy 4,000 of the best crossbowmen "on the pretext they had no need of their help"
For whatever reason, the clones didn't get there until most of the Jedi were dead. Thus, the Jedi didn't have any long-range support, and the Geonosians could fly around all day and take pot shots at them.
2 - There were too many of them, and too close.
Rogers suggests that the French at the back of their deep formation would have been attempting to push forward and quite literally add their weight to the advance, without realising that they were hindering the ability of those at the front to manoeuvre and fight, actually pushing them into the English formation of lancepoints.
Jedi need a lot of room to fight. If you're standing anywhere in front of a Jedi, you could very easily get shot in the back by a deflected blaster bolt. Plus, with all their running and jumping, stabbing each other was a real concern. It seemed to me like the Jedi started holding their ground better when there were only about 20 of them, and they could stand side-by-side in a circle. Until then, there were just too many of them, too much chaos keeping them from moving tactically.
3 - The location was awful.
At Agincourt, the French marched first, through a hail of arrows and mud to the knees. On Geonosis, the Jedi jumped into the middle of an arena and surrounded themselves with the enemy. There have been cases where Jedi have done similar things and survived, but combined with the other two factors the terrain only compounded their failure.
So, in summary, the Jedi basically walked into a killzone, where there wasn't enough room to fight effectively, and where there were no clones to help them. There have been many battles like the one on Geonosis or the one at Agincourt, where a superior force essentially walks onto the enemy's spears. Usually it's due either to incompetence or overconfidence; I'd wager the Jedi had a little of both at the start of the Clone Wars. But, just like the clones, the benefit of organics is that they can adapt and evolve. In future battles, we see a smaller number of Jedi fighting alongside clones, and (mostly) avoiding being stupid. Which seems to work much better for them.
Also, I think there's a good comparison to be made between English longbowmen and Super Battle droids, but I don't know if it helps my argument.
