so i just want to know if it can be reliable to reset the level mid-level like floor 2 of Death Wish if I got bad RNG(like alot of enemies have DB)(i hate DB)

yes
Double Barrels are run killers and Corey DW is a big part of any possible time save in DW along with Alex & Ash. I usually just see if I can get anything going if I get shotgunned and barreled but I usually can't and reset after I die. Mark DW is relatively consistent so it shouldn't be too much difficulty getting back to Corey DW at a good pace

Other levels depends. It really depends on where time can be saved. A slower Dead Ahead floor 2 due to bad RNG isn't reset worthy due to the mass amounts of time that can be saved on Floor 5 for example.