Bleach has a well-defined combat system primarily based on Zanpakuto, or soul-cutting swords, though many characters also wield unique powers and abilities in the heat of battle. The best-balanced characters often perform well, like Captain Byakuya Kuchiki, who has enhanced speed, swordplay and kido spells. But even the weakest of Hueco Mundo's Espadas could give the captain a run for his money.
The ten Espadas are Sosuke Aizen's minions, the most powerful Arrancars of all. They are all a major threat to the Soul Reapers, but not because of basic combat abilities. When they release their Zanpakuto, they gain unique powers and abilities, and that is where their true strength lies.
Speed Is One of a Soul Reaper's Greatest Weapons
Many of Bleach's characters are effective combatants because of how fast they can move, or because of how advanced their sword technique is. Among weaker Soul Reapers, this counts for a lot, since they have few kido spells and no Shikai or Bankai forms to rely on. During the early episodes of Bleach, even Ichigo mainly relied on his immense spiritual power and improvisational skills to fight. Before long, though, Ichigo became outclassed when his opponents brought out unique abilities against him, along with their quick movements.
For instance, Ichigo nearly died when Byakuya performed a Flash Step and slashed him across the chest. Speed was the deciding factor in that match, and after Ichigo trained a great deal with Kisuke Urahara and Yoruichi Shihoin, he became fast enough to face Byakuya on equal terms and block that Captain's sword strikes. But this power scaling backfired when the Arrancars were introduced.
At that point, "I'm fast" was no boast for any character. Every worthwhile character was quick on their feet, from Uryu Ishida to Nelliel the friendly Arrancar to Grimmjow Jeagerjaques. For the Espadas to stand out and get the edge on their Soul Reaper enemies, they'd need their unique Hollow abilities, not their speed.
The Espadas' Strange Abilities Are a Boon Against Soul Reapers
At first, a few clever sword moves and quick feet could win a battle, but when the Hueco Mundo arc began, having Bankai-level speed was only enough for a character to be taken seriously, not win. As new threats, the Espadas boasted not only regular Arrancar moves like the Sonido and Cero blasts but their own trademark abilities. Some of these Espadas could use those talents while in sealed form, but all of them gained unique powers after releasing their Zanpakuto.
Szayelaporro Grantz, Espada #8, is one of the best examples of this. With his swordplay, he can keep pace with Renji's Shikai, but his real advantage came from his mad science. In released mode, he could study and nullify his opponents' moves, which let him disable Renji's Bankai and Uryu's spirit bows. When his Zanpakuto was released, Szayelaporro dominated the battlefield with his myriad abilities, from duplicating his enemies to controlling them with dolls.
He fought Renji, Uryu and Nelliel's ex-Fracciones all at once, and he didn't go down until Captain Mayuri Kurotsuchi came along and beat him at his own game. At no point did Szayelaporro need to block an enemy attack or dodge with his speed.
Then there's the 2nd Espada, the fearsome former king of Hueco Mundo, Barragan Luisenbarn. He controls time and old age, rotting any flesh, energy or matter that came too close to his deathly aura. This gave him a huge edge over the assassin-like Captain Soi Fon, without even needing to dodge or throw a punch. Once he released his Zanpakuto, Arrogante, Barragan became a black-robed Vasto Lorde whose death aura extended even further, and he could also release the Respira technique to rot away his foes from afar. Once again, Barragan didn't need speed or fancy swordplay to outclass his foes. It would be disappointing if the #2 Espada relied on such basic techniques.
Ulquiorra Schiffer struck a balance where all this is concerned. While Grimmjow and Nnoitora were basic fighters, even in released mode, Ulquiorra had a few tricks up his sleeve. He could throw highly explosive lightning spears in released mode as well as the overwhelming Cero Oscuras, and his incredible speed was merely another tool in his arsenal, not his selling point. Ulquiorra also gained a long, flexible tail and bat wings in his released form, and most notable of all was his rapid regeneration.
In sealed form, Ulquiorra was just another swordfighter (albeit an elite one), but in released mode, he could do more, and that was what allowed him to triumph over Ichigo until the latter shocked everyone with his own Vasto Lorde form. By contrast, characters like Grimmjow, Nnoitora and their respective Fracciones seem oddly bare-bones. So what if Grimmjow is fast and hits hard when Barragan has a death aura and Zommari Rureaux can control people like puppets with his 50 eyes?