Murky vs Genji
Genji is certainly a pain to deal with and can certainly one shot Murky with his swift strike. However Genji has such a low health pool that Murky has a chance of dealing with him. You also need to be careful that Murky does not kill himself when Genji uses reflect.
For Gengi I recommend running slime build but substituting in Slippery when wet and Octo-Grab talents. Slippery When Wet lets you get to an injured Genji and Octo-Grab lets you lock him down for the team to finish off.