Khopesh is 17-20/x3 crit profile which is a 35% increase to base damage 0.75 + 0.2(3) = 1.35.
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This code block explains where the 0.75 + 0.2(3) comes from if you understand it then you can skip this block
Let's assume your base damage is 6[d10] +67 = 100 average
A Khopesh Frits on 17-20 at times 3 damage so
05% of attacks are misses (rolls of 01)
75% of attacks are normal (rolls of 02-16)
20% of attacks are criticals (rolls of 17-20)
This means our average damage per hit is
0.5(0) + 0.75(100) + 0.2(3)(100) = 135 avg dmg
35 is 35% of our base 100 damage
With perfect two handed fighting glancing blows do 60% of base damage on 75% of attacks this means it's an increase to base damage of 45% (0.75*60% = 45%)
So with a crit profile of 17-20/x2 and PTHF you would be increasing base damage by 60% (17-20/x2 is a total of 15% increase from base 0.75 + 0.2(2) =1.15)
With only weapon prof bastard sword does an additional 20% damage on 50% of attacks so a 10% increase to base, for a total of 25% increase to base when adding crit power so at one feat bastard sword is behind khopesh.
THF gets the B. Sword to 30% increase from base
ITHF gets it to 35% of base which is equal to a khopesh
So it takes 3 feat (Weapon Prof, THF & ITHF) to get Bastard Sword to the same level of power as a Khopesh with a single feat.
Note this math ignores the AoE aspect of glancing blows and doesn't factor in the d10 vs d8 difference it just looks at the % power increase each weapon gives. These should be taken into account when making a final selection.
IMO yes bastard sword can be justified assuming you can justify the feat cost.