OP, instead of reading too much into rejections, I think a better idea would be to talk to anybody you know that works in the field (preferably some senior person that knows the industry) and talk the interviews through and drill down to what is going on. Final rounds tend to be more about personality matches, particularly for trading roles, and someone that works with traders would be able to tell you what it is that you're saying/doing wrong from meeting you pretty much within 5 minutes. This isn't something that can be judged on a forum, but needs to be face to face. Finding such contacts could be hard, but it could really cut the mustard for you.
If you've gotten to 6 different superdays, chances are that the problem is something that's easily remedied and that you'll get more superdays. I'd doubt it's issues with your suitability for being a trader. And even if it were I'd highly doubt that you need to look at roles in other industries - it would be more about tweaking which types of trading or finance roles you target.
Again don't read into how many failures you have or how long it takes - until you're 100% sure what you're doing you won't get hired no matter how many trading roles you apply for (you really can't chance your arm to get into finance). It's not about 'keeping yourself positive' vs 'giving up' - it's about being smart about it.