I find it odd that Explosive arrow gets a GUARANTEED trap

[Vahnkiljoy]

Meanwhile arrow rain is just at % chance, seems a bit powerful imo for the insane ease of use.

[Peredur]

You can increase the number of volleys of Rain of Arrow up to 4.
Each volley can have up 40% chances to place a trap.

So you have 87% chances to place at least 1 trap.
You have 52% chances to place at least 2 traps.
You have 18% chances to place at least 3 traps.
And you have 3% chances to places 4 traps.

High Explosive Arrow has 100% chances to place 1 trap.
You are guaranteed to place a trap but also guaranteed to not place more than one.

Moreover, Rain of Arrow cd is shorter.
And Rain of Arrow can pull enemies to allow more are hit by a trap.

Anyway, if you want to use traps, you kinda have to use both skill.
The only alternative to one of those two is the first skill that can place a buff to increase damages from trap, but it's less effective than placing more traps (as you can have the buff increasing traps damage from other traps near it).

[Lvl99Chocobo]

It actually says Traps can only drop from the first volley though.