Disinterested Third Party
There are those (most) who will tell you that seniority is life itself, or tha tyou live and die by seniority, which is of course, bull ****. Seniority does determine what and when you can bid and get an aircraft, a seat (left seat), base, etc, as well as your schedule and some things you can do with your schedule (depending on where you are employed). Rest assured, however, that if you do not have the highest possible seniority number, you will not die, nor will it bring the dead back to life. It'sa number, and in a field of sixteen thousand plus employees...that's all it is. Just another number.
Your earning potential at a regional is diminished over your career, compared to a legacy. You may find, however, that there are degrees of sacrifice which one is willing to make in order to haunt the vaunted halls of financial valhalla. The buzzword a few years ago that had to be included at least twice in every sentence on this site was "QoL," which is teen-speak for "quality of life," which isn't necessarily a function of seniority, but depending on one's fantasies and goals, may be aided by one's seniority.
One of the least desirable aspects of airline life is commuting, and many hold as their goal the ability to not commute. If one can fly from one's base, one simply drives to the airport and operates a flight, without the need to beg one's way while hopscotching across the country to get to and from a base far from home. Seniority is part of the magic sauce that enables one to eventually bid to be based at or close to home. The strategy to accomplish that is a chess game of bidding the proper equipment, seat, schedule, and base, not necessarily in that order.
There exists in the legacy world a tiered pay scale that varies with aircraft type, broadly narrow-body vs. widebody, and the path to the widebody world ("WB" in teen-speak) involves being senior enough to achieve celestial nirvanah. For many, that may mean leaving one's home-base to grab the big, brass ring, until seniority brings one home again via the mystical chess game of the senior piece.
Your whole career, however expansive it may be, is achieveing one high somewhere to start oversomewhere else and work your way up again. In today's artificial, insular world, perhaps it's just a few hopscotches up the ladder; for many of us who have been around the block more than twice, it's a few more than that. Get used to it. One day you'll be the smartest guy in class, and the next you'll be starting a new class as nobody. Life's like that. So is aviation.
Don't overthink it. Don't trade life for a seniority number, either. Use it, when you get it, but it's not everything, and you can burn up your life chasing it.
Remember: man wasn't made for peanut butter. Peanut butter was made for man.