Boddhisatvas are still slaves to their compassion, yes. Their last relationship is that of compassion to everyone else, and their last mission is that of helping all sentient beings to achieve Nirvana. It is considered an imposssible mission, not just because sentient beings are many, but also because this is part of their delusion, and for as long as they believe themselves and others to be separated by Nirvana, it will remain so. So they are not fully whole yet. They need to take one final step and jump into complete aloneness to become a Buddha. Buddhas don’t see a difference between Nirvana and Samsara.