Not going to lie you lost me when you said ambush doesn't work with burst and to take trap expert.
Trap Expert is a must if you don't want Lurker or Native Hunters and such circle around and even disarming your contraptions below effective 120-140. It's like Interloper for Stealth. You can dash close to an enemy and deploy traps faster before they notice you, stopping them immedaitely - gaining much better distance advantage. Also able to depoy traps around patrolling enemies as well. It's a night and day difference and I assume you never tried it.
I will give you an example of what pistols are capable of, and you can tell me if they wouldn't completely overshadow the sniper part of a sniper/pistol build.
https://youtu.be/f-GyGQBN8s0
Again, you are trying to reason with a dedicated pistol build when the topic is sidearms for a dedicated sniper build. Since this is the 4-5th occasion in a row now, at this point it's safe to assume that you have either far below average comprehension ability, or intentionally sticking to this for a lack of better option and play dumb, knowing that you are loosing the argument otherwise.
Att this point, I could only repeat myself. Have fun continuing to argue with yourself with made up conversations.