While not AS specific, I've been through the song and dance of applying to just about every major (except AA) over the years and these are the things I've seen and heard. Oftentimes, it very much comes down to how well someone can interview and how well they perform on the entrance exam. Obviously this doesn't translate to quality, but the cracks usually show early on. Yeah, it takes the spot of those who could be better fits, but that's just the name of the game.
Personally, I also recommend having a professional review your resume or spend some time on r/resumes. HR people (who have no idea what this job is or what it entails) are usually the first ones to look at an applicants resume. Not having a Applicant Tracking System (ATS) friendly resume can and will get you an automatic TBNT. Some airlines have DX management claim to hand read each resume, but most have their HR deal with it, and AI resume scanning software is becoming more and more prevalent in the HR space.
I think it's naive to assume that nepotism doesn't play a roll, but I also don't think it's nearly as bad as some paint it to be. Connections can and do help, so if you're not networking or keeping up with those working where you want to wind up; you're doing yourself a disservice. On the other side of the coin, (to a point that's been beat to a pulse on here) your reputation can and will proceed you. I'm not saying it's the sole reason for people not making it to where they want to be, but if you're going on 5 years at a regional with no luck, maybe take inventory of your time there and how many people can vouch for you, because bad gas travels fast in a small industry like this one.
Lastly I think it's important that people look at the numbers. Every time any airline opens up, they get inundated with applications and nobody knows the crystal ball as to how or when they schedule interviews relative to when someone applies. It's also worth noting the growing trend of internal hires making up a larger and larger chunk of new hire groups, which makes being an external that much harder.
Happy Holidays JC DX people!