No, I mean for the same exact job. But even taking in account a 3 year upgrade, its worth running the numbers.
While yes, at present the upgrade at a major is about 15 years, it should conservatively be around 10 years for someone hired today.
Likewise, I wouldn't expect the upgrade to hold steady at 3 years for a quality LCC like Spirit either. According to APC - JetBlue is hovering around 4.5 years, Virgin 4.5-5 years, Frontier 8 years, Spirit 3 years, and finally Allegiant 2 months (great for the masochists).
When I ran the numbers given a 10 year upgrade at DAL (staying only on the 320) vs a 3 year upgrade at Spirit based on a 15 year career the numbers were very close, only about $180,000 advantage to the DAL guy, not counting 401k or other bonuses. Admittedly, that's really close spread across 15 years, 1,000 hrs pay per year.
But, if you end up somewhere that pays less than Spirit, do not upgrade within 3 years, stay longer than 15 years , or fly larger equipment at a major the gap widens and keeps growing.