I don't think that's correct.
Kirksey got 4 yrs, $38M.
http://brownswire.usatoday.com/2017/05/30/browns-sign-christian-kirksey-to-contract-extension/
Hightower got 4 yrs., $43.5M
http://www.espn.com/nfl/story/_/id/18915061/donta-hightower-returns-new-england-patriots
Kirksey got $1M more guaranteed ($20M/$19M), but that's pretty irrelevant given that both would be expected to play out those contracts anyway. Also, Kirksey is 2+ years younger, and entering his fourth year in the league to Hightower's sixth.
In 2015, at age 25 and in his 4th year,
Hightower had 3.5 sacks, 51 tackles, 10 assists.
In 2016, at age 26 and in his 5th year,
Hightower had 2.5 sacks, 31 tackles, 34 assists.
http://www.pro-football-reference.com/players/H/HighDo01.htm
In 2016, at age 24 and in his 3rd year,
Kirksey had 2.5 sacks, 93 tackles, and 50 assists.
http://www.pro-football-reference.com/players/K/KirkCh00.htm