Think they have way more cap space than you appreciate:
CapFriendly.com Armchair-GM User-Generated Roster
FORWARDS (12)
Right Wing: Mitchell Marner ($10,903,000) - William Nylander ($11,500,000) - Bobby McMann ($1,350,000) - Calle Järnkrok ($2,100,000)
Centre: Auston Matthews ($13,250,000) - Pontus Holmberg ($800,000) - John Tavares ($11,000,000) - David Kämpf ($2,400,000)
Left Wing: Matthew Knies ($925,000) - Nicholas Robertson ($1,350,000) - Easton Cowan ($904,667) - Connor Dewar ($800,000)
DEFENSE (6)
Right: Christopher Tanev ($4,500,000) - Jake McCabe ($2,000,000) - Conor Timmins ($1,100,000)
Left: Morgan Rielly ($7,500,000) - Brady Skjei ($7,500,000) - Simon Benoit ($1,350,000)
GOALTENDER (2)
Juuse Saros ($5,000,000) - Joseph Woll ($766,667)
BURIED (1)
Ryan Reaves ($200,000)
DETAILS
Roster Size: 20
Salary Cap: $87,700,000
Cap Hit: $87,199,334
Even if they keep Tavares, Marner, Kampf and Krok they can still afford two top 4 D and a top goalie.
Cap Space: $500,666