It depends on how long the lines are. If there are not too many passengers the two lines merge and there is only one person checking passports and BPs. When there are many passengers they have multiple people checking.
What usually happens is: The priority line is pretty short, but then crew and wheelchairs gets priority over the priority line, there is only one or two checkpoints for priority and many checkpoints for the regular line.

At the end you typically wait longer in the priority line than in the regular line. Also the new body scanners are at the priority lines. They are significantly slower, which does not help.

CX in my experience does not escort, but you get a voucher for the priority line. Same for LH. QF and LX escort.