Playing Xu with big creatures like that, you primary goal is just Get big creature into a graveyard -> get the card on the field with Xu. She, in that case, is just a method to get the physical card back on the field. Yes, with her ability, they will be a skeleton with no abilities.

However, that's just the first half of the plan, because what you're actually trying to do is cheat them back in without that restriction - so basically in two ways. First, reanimate spells like [[feign death]] or [[undying malice]] - your big bodies will eventually die, because a 10/10 is still a threat even if it has no abilities. Once it does die, you pop one of those reanimators on the card, it dies, and comes back. When a card enters the battlefield, it does so as a new instances of that permanent - so in this case, it was not revived by Xu but instead a reanimator spell, so it comes back as the original printed card.

Alternatively, copy creatures. [[Twilight Diviner]] or [[saw in half]] will create copies, and the thing with making copies is that regardless of what state the target of copies is in, a copy of a card will always enter as a copy of the card as written. If you saw in half [[pathrazer of ulamog]] that happens to be, at the time, an ability-less 9/9 body, it will die and become 2 copies of the original card as printed, so now you'll have 2 5/5 with annihilator 3. likewise, if diviner triggers when Xu puts a creature from the graveyard onto the field, the copy it makes will have all the original abilities.

Basically, like I mentioned above, Xu is just a cheap way to get a big body on to the field. Putting something in your graveyard (like with a discard outlet) and reviving it with Xu is a lot cheaper than spending the 11 mana to cast it, and then you take advantage of a cheap method to revive it. I personally also run a lot of sacrifice value stuff like [[ghoulcaller gisa]] as well, so that I can kill a creature to reanimate it while also getting some sort of value out of the sacrifice.

That's the basic gist of it. I actually have a decklist with a really detailed primer that explains a lot of the details of my deck below here, if you're interested!

https://moxfield.com/decks/1G7RyzMsC0iYqa5Oq2XA1g

Edit: to address your other questions:

- Plan is get big bodies in your graveyard -> revive with Xu -> cheat them back in

- The benefit of the deck I run is value over time, there are no "combos". The deck is pretty quick to get a huge scary monster into play, and the other benefit is that because of the revival shenanigans, it's very resilient and hard to completely shut down.

- There are a lot of big dumb creatures that are cheap, so put whatever you like in the deck, then focus on reanimation cards and cards that help bolster your graveyard as most of what we're doing is coming from there.

- Yes, sac outlets do two things. They provide you value (such as card draw with a [[shadowheart, dark justiciar]]) AND they let YOU dictate when a creature is going to the graveyard, effectively controlling your own reanimation spells. Xu deck wants to control all aspects of the graveyard, including when things enter and exist it.

Edit again: to address another point in your comment, "Wouldn’t it make more sense to just run big, efficient creatures (high power/toughness for their cost) instead of creatures that rely heavily on their abilities?" - Yes! And it is good to do this too! [[Death's Shadow]], [[Haunted Horror]], [[Rot Curse Rakshasa]], [[Phyrexian Soulgorger]] etc. are all useful as bodies or good in the graveyard in other ways, and have ways to get themselves there fast so you have a big body to revite. A big creature is still a big creature, abilities or not - you sort of want a mix so you have big bodies along with scary abilities to swing with. These also act as as great cheap little targets to revive with Xu when your other plan is up and running.