Spoilered for off topic

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Just computing average damage for the rogue posted for ease of comparison. I'm trusting the numbers provided are accurate, and not going through the build line by line. Though I am curious, why use daggers instead of short swords? Having d6s for weapon damage instead of d4s would make it easier to condense stuff, and been marginally more effective assuming everything else still works with it.

Going with an enemy that has an AC of 40, because that's a decent middle of the road level 20 AC.


Attack routine with haste is: +44/+44/+44/+39/+39/+34/+34/+29

1d4+13d6+45 (average: 93, crit: 143.5) on 5 attacks, and 1d4+13d6+43 (average: 91, crit: 139.5) on 3 attacks.


Main Hand
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Attack 1, 2, and 3:
10%: Crit Threat, 95% confirm (143.5), 5% not (93), average: 140.975
85%: Hit. Average: 93
5%: Miss. Average: 0

Average Damage per Attack: 93.1475

Attack 4:
10% Crit Threat, 75% confirm, 25% not, Average: 130.875
65% Hit. Average: 93
25% Miss. Average: 0

Average Damage per Attack: 73.538

Attack 5:
10% Crit Threat, 50% confirm, 50% not, Average: 118.25
40% Hit. Average: 93
50% Miss. Average: 0

Average Damage Per Attack: 49.025


Total Mainhand average damage: 402.0055



Offhand:
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Attack 1:
10%: Crit Threat, 95% confirm (139.5), 5% not (91), average: 137.075
85%: Hit. Average: 91
5%: Miss. Average: 0

Average damage per attack: 91.0575

Attack 2:
10%: Crit Threat, 75% confirm, 25% not, average: 127.375
65%: Hit. Average: 91
25%: Miss. Average: 0

Average damage per attack: 71.8875

Attack 3:
10%: Crit Threat, 50% confirm, 50% not, average: 115.25
40%: Hit. Average: 91
50%: Miss. Average: 0

Average damage per attack: 47.925


Total offhand damage: 210.87


Total damage with two weapon fighting: 612.8755



Now as a point of reference, two weapon fighting has a -2 penalty to hit, so without it, the last two main hand attacks would be altered as follows:
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Attack 4:
10% Crit Threat, 85% confirm, 15% not, Average: 134.225
75% Hit. Average: 93
15% Miss. Average: 0

Average Damage per Attack: 83.1725 (+9.6345)

Attack 5:
10% Crit Threat, 60% confirm, 40% not, Average: 122.1
50% Hit. Average: 93
40% Miss. Average: 0

Average Damage Per Attack: 58.71 (+9.685)


Total Damage gained from losing the -2 penalty: 19.3145.


This means that for two weapon fighting to not be viable, you need to find 3 other feats that combine to adding 191.5555 damage to the rogue's full attack.

Seems like a pretty tough sell to me.