I'm not sure why this is considered nuanced. It was a solid character but really boils down to him playing the 9/11 card to death. Slightly different from the normal "I hate USA" foreign heel schtick but still in heel 101 territory. Tap into some degree of the truth, be shitty about it and abuse it for boos. Cactus did it with the anti-hardcore thing, Jericho did it with his last honest man schtick, Austin did it when he went psycho in 2001 and claimed he never asked for the approval of the fans. On and on it goes. It's not nuanced, it's not great, it's just one of many ways to get heat. End result's the same sometimes, no matter whether you adopt the so called cheap route or not.
Anyway, the fact that he quit the business once his WWE run didn't work out tells me that they dodged a bullet, things worked out for the best. You can't invest in someone on a long term basis if they're only invested when things are going good. The guy was a flash in the pan, one of many.
He might have been brought back eventually if he had stuck around. Daivari was able to adapt and keep adjusting over the years with multiple clients and even as a wrestler. I don't blame Copani for doing what he felt was best for him because he didn't owe shit to anybody but regardless, in the bigger scheme of things, it was good for the company.
Plus he was boring as fuck in the ring, had no identity in terms of style and while he could get heat, the promos really weren't as good as they're made out to be. The basic material was good and an easy pressure point but delivery wise...hokey cringe crap. He would have been completely exposed once the initial buzz wore off. Already was, really. He wasn't quite all that back in the day as far as general IWC reception goes.
I'm pretty sure that the only reason he even has such a cult following is because he didn't reach his full potential. If he had he would have been lumped into the "they shoved this guy down our throats, generic foreign heel, fuck WWE" category by the same people who sing his praises now.
The timing was as right as it was ever gonna be. 4 years removed from 9/11....not too close to be enough of a problem and not too far removed to be considered outdated. But regardless, it would have always worked. It's such an easy thing to exploit that it will always work in terms of reactions in the US.