See above^^^
If your career goal is 121 flying at a major, nothing will get you there quicker than 121 flying at a regional. Pass rates in regional training are quite high, the company’s WANT YOU to pass and will generally work with you to assure that result for anyone motivated and making the effort. The majority of those who do not pass, in my experience, fail because of alcohol, social, or motivation related problems and only very rarely do you see failures from just a lack of aptitude.
And while the retirement wave (and hence the hiring wave) at the legacies will be going on for most of the next decade, seniority is everything in this business. Delaying your hiring by one year may mean 900 additional people have a better schedule than you do for the next 30 years.