I don't care where they rank. I was merely referring to their ability to defend against the opposing forwards. Your top pair, Mantha and Lowe are all guys I would say are at least plus defensively at this level.
There are questions about Patrick and especially Liapkin but overall I'd say you're OK.
I do have one concern about your blueline, particularly the top pair. It has often been said that Laviolette requires strong skating defensemen who are really adept at moving the puck out of the defensive zone for his teams to have success, because his system often has the forwards blowing the zone and leaving the defense out to dry. I'm not concerned about this with Patrick and Liapkin, but I would like to hear how your team will manage this when the other 4 defensemen have the puck.
Pulling some stuff from the bios
Gadsby
While playing with the Hawks, Gadsby established himself as a terrific competitor who was equally adept at leading a rush as he was on the defensive aspects of the game. Bill could be an aggressive player on the ice (a (clean) bodycheck on Tim Horton in 1955 broke the Leafs' player's leg and jaw, almost ending his career) but whose calm demeanour off the ice was a paradox.
-13x Top 10 in NHL scoring by a defenceman (1,1,1,2,2,2,2,2,4,4,6,7,7)
-12x Top 10 in NHL assists by a defenceman (1,1,1,2,2,2,3,4,4,4,7,8)
-11x Top 10 in NHL goals by a defenceman (1,1,2,2,2,3,3,4,6,6,9)
Clearly strong offensively as well as defensively classic two way D
Clapper
-Four times Top 5 in NHL scoring by a Defenceman (1st: 1941, 2nd: 1939 & '40, 5th: 1943)
No direct quotes about his puck handling ability sadly