IMHO, flying with the pilots doesn't matter, but the ME TOO does.
Giving up bid lines and bid sheet matter to me. Lines throw a little equalizer into scheduling. Think, with Pref Bid, by seniority everyone would bid off thanksgiving until it got to a certain number and then everyone thereafter would work thanksgiving. No SAP, no maneuvering, wham, you're done. Lines force F/As to really balance, do I want this crappy thing with Thanksgiving off or what if I fly this lovely international block and work thanksgiving. I don't want to go to Aunt Sally's anyway. Result? A more junior F/A flys the crappy block but gets thanksgiving off.
A simplistic example, but illustrative. PBS will primarily benefit the mega senior. The junior blockholder is looking at a life working weekends and holidays. The junior blockholder has 25 years.
I believe in seniority, however the system doesn't have to stack the deck quite so fiercely. What we have now is more merciful than that, and it's untenable.
The T/A must be viewed through the prism of being a total compensation package. Scheduling, "when it goes wrong" protections, sick pay, they all are just as important as the final dollar number of compensation.