"Any time I change my job, green card process has to be restarted from square one"
The most time-consuming part of the process is waiting for your priority date to be current. Once you have your priority date, restarting the process through another company shouldn't really make a difference, since you can just reuse the existing priority date instead of getting a new one.
Theoretically, you can lose your priority date if the previous company cancels your I140. But since it costs thousands of dollars to do that, most companies don't bother.
The most time-consuming part of the process is waiting for your priority date to be current. Once you have your priority date, restarting the process through another company shouldn't really make a difference, since you can just reuse the existing priority date instead of getting a new one.
Theoretically, you can lose your priority date if the previous company cancels your I140. But since it costs thousands of dollars to do that, most companies don't bother.