Lowering the difficulty level to breeze through the game is one thing, but blaming it on the interface being 'clunky' just feels like a cop-out. Think about it, in a street brawl with multiple opponents, the scenario you described is pretty much what you'd face – when you engage the one in front of you, the others are likely to strike from behind. It's not an interface issue; it's an objective reality of the (game) world.
Have you considered that maybe you're approaching the game the wrong way?
I'm halfway through the game, and every time I've faced multiple foes, I quickly realized that brute force with bullets and batons wasn't the answer.
Instead, I had to get smarter, utilizing the environment, explosive canisters to weaken the enemies, tossing one over a railing to deal with the monsters, and launching monsters on spike walls.
I'd recommend giving normal difficulty another shot, but this time, try playing Callisto Protocol, not Overwatch.