Kylington's numbers were better than Sandin's last seasonnin essentially every sense, while the Flames defender also saw time in the top-4 last season. Kylington has 168 career games played versus Sandin's 88 in mostly bottom pairing minutes. Kylington's deal will very likely limit just how high Sandin's camp can push.
It has been reported that Sandin was offered a similar deal to the one tabled to and accepted by Timothy Liljegren, a 2-year, $2.8M deal ($1.4M AAV). An annual average between Liljegren and Kylington, maybe $1.6M and $2.1M for two years would be fair value for Sandin. With no arbitration rights, the Leafs' only concern would be an offer sheet for Sandin, but if it hasn't happened by now, the chances of it happening are not overly high.
With the Leafs already $1.5M over the cap, they will still have to move out a player or two via trade to fit any new deal for Sandin onto the roster. The work for Dubas is far from over for the off-season.