I strongly disagree but I do think the story and worldbuilding can be extremely overwhelming at times. I really enjoy the themes and scope of the Pillars of Eternity universe and I don't think it is too difficult to grasp if you give yourself enough time to take it all in. A lot of the questions you pose are answered for the first time in POE 2 as you progress through the game. Maybe I can help though.
MAJOR POE 1 and 2 Spoilers below!
1) It is understandable if you are confused here if you did not complete the story of the first game or do not remember it well. The story of the first Pillars of Eternity dealt with the Hollowborn crisis; Children were being born without having what we would call a soul. They were like empty husks. The reason for this was believed to be a curse from the god Eothas, who had inhabited the body of human named Waidwen and began a rebellion to reveal the truth of the gods and end their control over everyone on the planet. The rebellion was ended after intervention from the other gods, and superstition led to people blaming the births of soulless children on this rebellion. In truth, it is discovered in the first game that the gods were created by an ancient race of humans called Engwithans, using a science called animancy. The Engwithans had mastered the sciences and wanted to find proof of gods, but they failed to find any. Using animancy (which is basically a kind of soul manipulation science), they created their own gods with which to unite all Kith (the playable races) under. The engwithans sacrificed thousands of souls to a machine that melded them together into 11 different gods that would guide mortals and give life meaning. They created the cycle of rebirth, another complex animancy machine to allow for souls to be reincarnated. Throughout the ages, the Engwithans and their sciences disappeared primarily due to time and the obfuscation and manipulation of an organization called "the Leaden Key" which works to preserve the secrets of the gods and Engwithans and preventing Kith from understanding the true history. The main antagonist of the first game is a wizard named Thaos, who retains the memories of his original self throughout all of his reincarnations, as an an ancient Engwithan that leads the Leaden Key and was present when the gods were born. He is partnered with the god Woedica, who conspires with him to keep all Kith and Eora (the world that the games take place on) in the dark. The actual promise you are referring to in the intro of POE 2 has to do with what the Watcher decided to do with all of the souls of the Hollowborn. Berath (god of death and reincarnation) wishes for you to return the souls to the reincarnation cycle. Hylea (God of the Sky, Maternity, Beauty, and the Arts) wishes for you to return to the souls into the bodies of which they were intended. Rymrgand (God of Entropy and Famine) requests that you destroy the souls and end their existence. Galawain (God of the Hunt and Survival) wishes for you to use the souls to strengthen only the Dyrwood (location of POE 1). Skaen (God of Rebellion and Schemes) wishes for you to use the souls to empower Woedica even though that's kinda what you were fighting against in the first place. Wael (God of Mysteries and Illusions) wishes for you to just randomly scatter the souls just for fun.
2. Eothas is very vague on his plans until you meet him at Magran's Teeth. The other gods were unaware of his intentions but feared that whatever he had in mind was not in their best interests. As the Watcher, you are being entrusted to seek out Eothas and report to the other gods what you have learned. Eothas is the God of Light and Redemption, and is the god that cares the most for mortals (though Hylea also seems comparatively benevolent). As mentioned in the last paragraph, he inhabited the body of a human named Waidwen, attempting to reveal the truth of the gods and free Kith from being at the mercy of their whims. It did not work out for him. Between the two games, he inhabits the gigantic statue at Caed Nua (which was the castle ruled by the Watcher in the first game), destroying the castle and absorbing a piece of your soul. This is where the beginning of the 2nd game comes in, with Berath rescuing the remainder of your soul and tasking you with confronting Eothas. Eothas is traveling the Deadfire absorbing power from those big green crystals called Adra, which are somehow connected with soul energy and used in animancy. Eothas is also absorbing power from the souls around him, making himself strong enough to ultimately complete his goal. His ultimate goal is to destroy the Engwithan wheel of reincarnation, which will result in the gods losing much of their power, largely freeing Kith from their rule and forcing them to rely on each other. Eventually, both you and the gods realize that he is unstoppable, and it is up to you to reason with him. In your final confrontation with him, it is ultimately up to you to convince him of what the right thing to do is. You have a lot of options here, and the consequences are largely unknown but the ending slides do offer a little bit of information about the post-game. It is unknown what the gods will do in retaliation, but it seems as though some of them accept the eventuality if not somewhat siding with Eothas at the end.
3. Xoti belongs to a religious organization called the Dawnstars that worships Eothas, and she specifically focuses on a manifestation of Eothas that she calls Gaun. Xoti believes that Gaun is the "rebirth" aspect of Eothas that is the statue that has returned to the Deadfire. She has been having dreams about what Eothas/Gaun is doing and believes it is her purpose to shepherd the souls that Gaun is leaving behind back to him so that they can be reborn. I have to admit I am personally unclear as to whether she is really doing anything with the lantern and exactly what is happening when you take her to interact with the adra. The souls seem to be following you rather than Xoti's lantern. She does have some dialogue with Eothas if you have her with you in your party when you encounter him at Magran's Teeth and at Ukaizo. He mostly focuses on all the good that the Dawnstars have been doing for their fellow mortals, and that mortals will look to kind hearted people like her for guidance in the future.
4. Eder was actually a follower of Eothas, but his belief has been shaken after learning the truth about the gods in POE 1. He looks up to the Watcher and whatever you have to say can shape his mind within the game.
A lot of POE 2 relies on choices you made in the first game and it is regretful that they don't provide you with enough information to understand the load state that you select to start a new character. However, you can learn quite a lot while playing the game and your second playthrough can give you much better insight into the lore of the world so that you can make better informed choices. I absolutely think that it is worth it, because the world of Pillars has a very grand and features interesting stories worth learning about, and the failure of Obsidian to properly prepare new players doesn't negate the quality of the writing.
