Two more possibilities... some of the FO's you talk to may not upgrade ASAP. I waited a full year after I could have upgraded for better QOL. If money isn't an issue, senior FO life can be way better than junior CA life. Also, the stated upgrade times are for the most junior CA, which means the most junior base. So say you live in IAH and fly for XJT. Most junior CA may be ONT and you're not willing to commute or move. So the upgrade time may be 3 years in ONT but 4 years in IAH.