Shes receiving mana from Sakura because she's sakura's servant

She doesn't need time to charge her excalibur blasts as long as she receives mana fast enough

Okay yeah in that case the only way I see someone else winning is if Gilgamesh summons either his ship of light or Vimana to evoide the blasts and open a portal right next to her to either take out one of her hands or hit her point blank with Noble phantasms as we have seen he can open portals as close or as far from his enemy and anywhere he wants.

Yeah GIlgamesh and Artoria in my opinion are the two top contenders but it's hard to tell which one is stronger when they could easily both defeat the other

Also it's weird having no Avalon because Saber is losing one of her strongest abilities and the reason her endurance is so high

I view it as fair as with Avalon it's basically the ultimate cheat sheet, I still remember were the plot deamed she win in her second fight with Gil and she magically gets Avalon and wins when the whole fight she was getting tossed around. But that's besides the point, If Gil keeps at range and surraounds her with portals and fires Noble phantasms she's doomed as he could fire anything and their effects would hit Artoria all at once ranging from poison, curses, fire, the phantasms exploding or any other random effect and she has no defence against that, but if he's in range of the blast he's doomed unless he has something to block it.

He probably has defensive Noble Phantasms able to handle Excaliblasts, since he doesn't meet the requirements to unleash Excalibur at the level it was at to bring down ORT, and he should have, say, the prototype for Achilles's shield, which, even if it can't fully take an Excaliblast, can probably take a lot of its power before breaking.

True as even with unlimited mana it doesn't mean all of it's power is going to be releaised as it's full power is only unleashed agasint things like Ultimate ones, ORT and Sefar. so Gilgamesh could very well use multiple defences to block Excalibur to buy him time to charge Enuma Elish which has been shown to be ridducaly strong, hell in Strange fake he would have destroyed the earth if Enkidu didn't use their Enuma Elish to put things back together.

Yeah, Excalibur only goes all out against targets that meet specific criteria, which Gilgamesh doesn't meet. He could maintain range to dodge or block her attacks while harassing her with high Rank treasures as he charges Ea to full power.

Is Saber in Fate Extra the same as Saber in Stay Night?

Be specific theres two Sabers in Fate extra/Extella that have the same face, but Artoria overall does seem to version of herself from Stay night considering her interaction with people like Iskandar and Gil, It could be a different incarnation of her.

If you mean the Artoria, no, they are different instances of Artoria. The Fate Artoria isn't on the Throne, so Moon Cell Artoria is a copy of her recreated from the Moon Cell's record of her.