If it's alright, can you give me some more pointers in how to get the leader ending? I am on Randall's path and I had high rep points with all houses (wasn't equally high but they were close enough) and I did tell Randal, the Iscari, and that Mavvar guy that I will unite LA but for some reasons, the "My rebellion" option has never came up. Did you perhaps maxed out determination and if so, how? Or maybe I'm not supposed to agree to Andrei's deal, I don't know. I have no idea what I'm doing wrong and it's getting tiring to go through his route over and over again just to get the leader ending. (Since I've already got all of Randall's other endings, including the special ending)
I would love to help you, but I'm not sure where you went "wrong" either. If you used the options to talk about it beforehand and have sufficient reputation with the factions, then I'm stumped as to what could be missing. But the deal with Andrei shouldn't be the issue, since I took that too. As for the personality traits, I'm not sure how they factor in, but since I played my Iscari as somebody who can take care of herself and isn't easily daunted, my character turned out indeed pretty determined, though the stat wasn't maxed. (Here are my exact stats at the moment of the proclamation oy my rebellion, in case anyone wants to take a closer look: https://imgur.com/zWpqiir) I wish I could be more of a help, but maybe someone else knows more?
That aside, are you trying to get Randal's second ending? Just asking, because I tried the very same thing, only to find out that it isn't linked to that at all. There seems to be only one ending for the rebellion, whether you side with Randal or go on to unite LA, and it even plays out mostly the same, with only minor differences in the epilogue. Spoilers ahead, for those who want to know: For the second ending, you have to side instead with Andrei, while also making a deal with Lazarus. At the end, you will notice Lazarus sneaking up on Andrei, just let him do his stuff.