Why Deadhead and not Longbow?
For whatever spaghetti code reason: Aptitude is additive at the end of the series of equations.
= Base Damage x ((1 + Serration) x (1 + Longbow) + (Aptitude))
Aptitude is just thrown at the tail end... and doesn't get considered in Longbow Sharpshot's multiplicative effect and is, instead, additive. That being said, Deadhead is additive to Aptitude as well, but the bonus is higher than Longbow.

Total Damage for this deadhead build @5 Statuses:
Damage Per Shot = 11,462,455.67
Electricity Status Damage/s = 34,600,855.25
Total Instant Damage = 46,063,310.91
Considering Status Chance:
Avg Damage Per Shot (0s Electric) = 26,213,346.59
Avg Damage Per Shot (6s Electric) = 99,967,801.19