From myself personally going through all the world bosses in the game solo, I've gotten to this point where I can safely say I know which two world bosses in the game are the hardest to fight, and for good reasons and why? Also adding on tips to make the fight against such bosses that much easier.

B'korgen in terms of power b'korgen can potentially hit way stronger than Zandadunoz the Reborn at the unfinished dolmen if you allow there to be way too many ads unchecked. Now B'korgen assortment of ads can interrupt you and make you get cc'd a great amount of times, enough to kill even majority of the more hearty individuals. The fight becomes a lot more easier if you are using builds adjusted to fast movement and also bomb builds, as those work wonders against b'korgen. Often you will be trying to kite the enemies on opposite end of the boss so you can place some bombs on the boss (inevitable detonation since you can pull multiples) The fear phase the boss does doesn't always mean it is a bad thing because more often the fear phase also keeps you more away from various ads that try to cc you, as the fear phase for some odd reason breaks their cc hold on the player. Also another thing to note is ALWAYS KEEP NEAR'ISH B'korgen, never allow yourself to be too far from the boss as the ads will break apart and you want the ads clumped up nearish to the boss so you can lay aoe on them and wipe them out quick as possible.

Now onto Zandadunoz the Reborn... the fight is a lot simpler once you realize it can be pretty easy. Simplest ways to deal with Zandadunoz the Reborn is speed for one, another is those portals... heavy attack them to break them... yeah targeting it can be a pain as the ads sometimes prevent you from doing that as they keep getting in the way (yeah I know it is annoying). Majority of the dangers of Zandadunoz the Reborn is because of the portals... like 95% of his dangers are his portals. Always try to deal with portals as they are a primary concern all the way till he is at 5% health. Play with your wards from time to time so you don't get over swarmed with the aoe the portals bring to the fray if you happen to step on them.

I've personally have done Zandadunoz the Reborn far more times solo than B'korgen and I can admit that B'korgen can be potentially more dangerous than Zandadunoz the Reborn by a longshot. But if B'korgen is by himself and if Zandadunoz the Reborn is as well (no ads like they don't have any ads at all) B'korgen would lose his shield and die very quickly, where as Zandadunoz the Reborn not so much. They both would be about the same danger where only difference is B'korgen would die far quicker than Zandadunoz the Reborn.

If anything else I can safely say that B'korgen is the hardest world boss in the game to solo. As things can go south really easily if things aren't handled right, Zandadunoz the Reborn can be a bit more forgiving where B'korgen is less so.

Are there any other tricks to these bosses any of you might have picked up that I didn't know or forgot to add?