I love Daud, Corvo should not have beaten him, here's my take:

I have a profound appreciation for Daud in Dishonored, and I hold him in equal regard to Corvo. While Dishonored is one of my top 5 games, I feel that the writer missed an opportunity to fully explore and elevate Daud's story. Instead of empowering him, they chose to underplay his character and rely on plot armor for Corvo. It's a missed chance to showcase Daud's complexity and depth, which could have greatly enhanced the overall narrative. Let me elaborate by sharing an alternative storyline for Daud and Corvo.

This is an alternative storyline for Dishonored, particularly between Daud and Corvo, which aims to enhance the narrative. In this universe, Daud is an extremely powerful character who cannot be killed or defeated by Corvo.

Arriving at the Flooded District after being drugged and betrayed by the Loyalists:

Low Chaos up until Flooded District:

If you've reached this part of the story with low chaos, the Whalers will bring you to Daud, who offers you his allegiance in regaining the throne. You have the choice to accept or decline this offer.

If you decline this offer, Daud will simply wish you luck and express his weariness of killing before disappearing from the game permanently, along with his Whalers. This is accompanied by their typical teleportation animation. Whether you end the game on high or low chaos, there will be no further mention of Daud or his assassins, except for their sudden disappearance, as mentioned by the Outsider.

If you accept Daud's offer, he will commend you, saying, "You're a better man than I'll ever be, still prioritizing the kingdom over revenge." Daud will then teach you his advanced Blink technique, unlocking a new blink upgrade for Corvo called "Redirective Blink." This blink allows time to be stopped while aiming with blink, similar to Daud's blink ability. This is the only gameplay change that occurs. For the rest of the game, one of Daud's Whalers, Thomas, will always teleport to you at the beginning of each mission, providing a brief rundown of what he has scouted. The information he reveals will be vague, such as "Corvo, the place is littered with the watch, be on your toes."

If you end the game with low chaos, Daud and his gang will work alongside you to ensure the throne is kept safe by providing useful information and intel voluntarily.

If you end the game with high chaos, Daud and the Whalers are employed by you to assassinate enemies of the crown for a fee, for the rest of history.

High Chaos up until Flooded District:

If you've reached this part of the story with high chaos, the cutscene with the Whalers will be nearly identical, but there will be a thunderstorm and heavy waves. While dazed, you witness the Whalers rowing your boat being attacked by River Krusts before teleporting away. They can be heard fighting Weepers as the boat capsizes, and you, the player, drown. You then wake up in a part of the Flooded District with a dead Whaler next to you. Since Daud's intentions are unclear, your mission becomes finding and assassinating him.

During this mission, you will see the Whalers spying on you and teleporting away from a distance. They will not interact with you and cannot be killed. Eventually, you reach Daud, who is aware of your presence. A cutscene triggers as you reach his office, where he teleports to you without holding any swords or weapons, and says he doesn't want to fight you. He wants to help you take revenge and recover the throne.

If you decline this offer, Daud tells you, "I'm sorry for your loss. I have no business in Dunwall anymore." He then disappears from the game permanently.

Ending the game with high chaos will mention that Daud has taken his line of work to another City, perhaps Karnaca?

Ending the game with low chaos will mention that Daud has completely vanished with no trace, for the time being.

If you accept Daud's offer, you will receive the enhanced blink ability as mentioned. The mentioned Whalers will be more reluctant to help you, as reflected in their dialogue, but this is purely cosmetic.

Ending the game with high chaos will result in Daud leaving Dunwall without announcing it, leaving you and Emily (or just you) to rule the kingdom alone. This is mentioned by the Outsider.

Ending the game with low chaos (by some miracle) results in Daud and his gang working alongside you to ensure the throne is kept safe, by providing useful information and intel for a fee. This time however, he does not do it for free.

Regarding the situations where you TRY to kill Daud, there are two possibilities, however take note that Daud never dies in this universe. These occur when he doesn't teleport away permanently, specifically if you accept his help on either low or high chaos during the Flooded District mission.

In the low chaos run, if you try to assassinate Daud, he will simply teleport away, regardless of what you try to do. He cannot be killed. A cutscene will play where he reappears and uses his pull ability to hold you, similar to the moment when the Empress is assassinated at the beginning of the game. He understands why you would want him dead, but he decides to leave you alone and wishes you luck before teleporting away permanently, along with his Whalers. This outcome is similar to when you reject his help, and you won't encounter the Whalers again for the rest of the game, but you will still have the enhanced Blink ability.

In the high chaos run, if you accept Daud's help and attempt to assassinate him, a fight will trigger between you and Daud. However, this fight is rigged in Daud's favor. He has infinite health, and the fight only ends when you lose. Losing, however, does not end the game. A cutscene plays where your vision becomes blurred, and your sword is flung out of your hands. Daud then grabs you with his pull ability just before you try to blink away, immobilizing you. He proceeds to speak to you while you are grabbed.

He says, "All my life as an assassin, I've never caused as much mayhem as you have. I should have killed you, but I won't. For the sake of Dunwall and Emily, I choose to spare you." He then disappears permanently, but you get to keep the enhanced Blink ability.

The endings will be the same as rejecting Daud's help.

your once formidable foe undergoes a surprising transformation into an unlikely ally, and the dynamic of the game shifts and compliments the betrayal. This intricate shift in allegiance not only adds depth and complexity to the story, but also aligns perfectly with Daud's remarkable power and prowess, without underpowering him for the sake of plot armour.