Sylus is just a lone wolf. 

He has Luke and Kieran because they've proven their mettle and strength to handle being around him and the dangers of being Onychinus's leader, but they're as much of a free agent to him as MC is. They're there because they want to be. 
Mephie is basically his familiar/go-go gadget all in one. He keeps no one, by choice (proven by his lines to MC about how she should be strong enough to stand by his side because he lives a dangerous life, and because he also does not need to coerce anyone to be in his orbit).  Everyone else around him are people who respect his position and power. 

Being solitary by choice ≠ being a loser