"quick upgrades" ? yeah, the Contractor FO's on the 737 will give you a better idea than me . . . .depends what you mean by "quick" . . .quick like Ryanair ? or quick like SAS ?
Anyhow, suffice to say , most Contract FO's who came from Ryanair did not find it sufficiently quick, and on the 787, well, you have still DEC's (same prob as 737 ) and CRZ Capts in the way (with the CRZ Capts suffering the same blight as the 737 FO's I.E DEC's )
Believe nothing you are told at interview, truly, don't .