If you show up without prior 121, yes. At any carrier upgrade will be an issue if you only have 1500 when you show up. Outside of the regulatory mins for an unrestricted ATP, there are "company mins" which are there due to insurance. The company doesn't care how much time someone has when a seat needs to be filled, it's what the regulations and insurance underwriters require... So if you need the FO time regardless of where you go... You might as well make the most money with the most seniority movement.