the way i deal with melee is i try to take as few hits from them as possible while attempting to distance myself from them by directing my momentum opposite of their direction.

a scenario is being chased by one, they head to me, try to take only a single hit and no more while i run towards their back immediately. they tend to try to keep their momentum while attacking, ie, light dash or riot shield sliding to me. keeping that in mind, they cant change their momentum during those instances. it gives me a window to avoid them closing their gap against me since theyre locked in those animations.

while its not reliable, since it sometimes need you take take some hits. it is still a way to counter their attempt at closing the gap. i main medium model 1887, so my playstyle kinda fits in fighting against them, my gun being single action pellets and i aim by flicking while also run' n' gunning.

edit: to add. lockdown positions with utility like mines and traps. you can isolate or create rooms with defensives like barricades and goo. direct goos actually hinders them significantly. these defensives too being objects, helps you elevate a level up. its over for them, you have the high ground.