It's certainly pretty pointless if you're running a gxbow build...
Also, I really liked insightful reflexes on mine while levelling, and I went pure, as I'm pretty sure the additional sneak attack > eternal knives. Crap maths from my crappy build:
3d6 sneak dice = 11.5 average damage from sneak.
24 RP - epic levels
16 (rounded up) average RP - zeal
12 RP - DC Cores
20 RP - Mech
1 RP - Tome (Haven't upgraded yet)
2 RP - Mythic from E Divine Artillerty
---
75 RP
11.5 * 1.75 * 1.5 = 30.2 average damage from sneak (which I basically get permanently due to assassins trick).
Knives is average 3.5 (spiked) + 11 (knife shot) = 14.5.
I still get that the 2 arti provides versatility with the dog + rapid reload + feat, but given that just the sneak damage trumps the knives, not to mention the 3 base damage, and the occasionally useful clicky, I'm pretty certain 20 rogue is better DPS. I may have missed something though. As I said, crappy maths is crappy... on a crappy build... from a crappy player
It's more than that. Pure means losing a feat. Which means losing 2 RP from WF. Which easily makes up that difference when an unoptimized build is critting for 3k+ and doing 300+ SA damage.
Also Magical Training and easier leveling are good for QoL.