Well no. You attacked him because you thought he was bribing you (When in fact it was the machinations of Chicane von Trubaldsome). Thring then offered to legitimize your kingship even after catching you attempting to burn/sack his city.
You would think that sort of action would lead you to believe that the Archbishop is in fact not a bad guy.
And to this day we don't know how big/badass Brighthall was. Or its troop disposition. But I'm betting on large enough. Do keep in mind it was hinted there were something like 11 Orthodox provinces. Elbreth was 2 Cyclist 1 Mirish Paganism(Counting Miring itself, which I doubt we would have kept very long), and the Weylands would have counted for 2 provinces of Mirish Paganism.
Yeah, That seem like reasonable odds to you? Even if they were small provinces we could have been in bad shape. And we know at least that Brighthall was some kind of large size.
Remaining apart means no trade, and constant tension with many nations. With no real solid relationship with Elbreth (You informed them of an attempt to bribe you, which they'd know or at least suspect was in fact Chicane, and not Suul), not to mention the practice of taking slaves, there would be few if any friends for Weyland without attempting to build some kind of commonality with nearby nations. The swiftest and surest path would have been to take the Archbishop's offer.
Otherwise? Lets add it up.
Spurning the Archbishop? Enemies with Orthodoxy. And potentially only one nation to recognize your kingship (Elbreth)
Cyclism is by its nature militaristic as evidenced by Grand Master Black. And as your aim was not Cyclism, No commonality with Elbreth, a guarded border is about the best case scenario there.
As hinted by the Archbishop, Brighthall was watching you. Closely. And without the shielding of the Archbishop via legitimacy, you would be invaded and your unification destroyed.
My opinion was that your successor would do whatever it took to ensure that the country you created survived, going so far as to pay token lip service to the Archbishop, and likely side with Elbreth if any conflict arose. I chose to explain it as no conflict arising due to Elbreth's success in the field during the demanded 'crusade'. As a result, the 'official' religion of the Weylands became Orthodoxy in said epilogue chunk. They would have ranged farther afield to gather the slaves that kept their society going, comfortable in the knowledge that they had solid allies nearby with ties of religion, recognized legitimacy and reasonable relations.