Romans 5:15 — But not as the offence, so also is the free gift. For if through the offence of one many be dead, much more the grace of God, and the gift by grace, which is by one man, Jesus Christ, hath abounded unto many.
Both Adam and Jesus Christ are heads, and their actions influenced those under their headship.
But while there are similarities between Adam's and Jesus Christ's headships, the dissimilarity is grace, which far surpasses the scope and power of sin.
Much more = legal certainty