One at a time, and most bosses can’t be PLed. However, this is an incomplete picture of PL.
With Converge, the PL creates a singularity, sucking others toward it and briefly stunning them. With Ruin, they are also slagged and shocked. With Helios, they are also hit with fire. While a target is PLed, you also get Wreck and Chain Reaction, which drive your damage output through the roof. With Cloudkill, you also create a corrosive cloud of substantial damage. For these reasons, Maya is among the best at mobbing.
When it comes to bosses, use the ads. For example, Son of Craw. Can’t PL him, but you can PL an ad to activate Wreck and Chain Reaction. Or, do as I do and take Thought Lock. That gets me Wreck and Chain Reaction, AND it turns the boss against his own ads when I TL them.