Alita is, quite frankly, faster than Saber by quite a margin.
Proof please? Saber's top movement speed is calced at about Mach 15 with at least double that for reaction speed.
Not to mention Alita can easily trick and/or distract Saber with Astral Doppelgangers
This sounds like something you're pulling out of your ass considering Alita's abilities in combat involve either melee or plasma manipulation with her Imaginos Body giving her greater abilities such as regeneration and the ability to perform and resist hacking, but nothing that involves astral projection.
Anything metal can become a weapon at Alita's discretion with her Nano-Corrosion.
And yet again, we exaggerate. Nanotech in the world of Alita involves hacking anything electronic and fucking up biological and mechanical beings on the atomic level with it, not controlling metal.
Avalon can give Saber higher defenses and great regen, but it doesn't help if there's nothing left to come back from.
Avalon guards against all attacks from the physical plane of existence, essentially making Saber invincible to all of Alita's attacks. It also reflects enemy attacks back at whomever targets Saber. Avalon's a much more potent defense than a mere barrier.