How do you play this game without enemies becoming damage sponges?

I started my first play through specializing in heavy armor and two handed, but by the time I was around level 10, fighting enemies just took too long. Enemies would take minutes to kill and I usually ended up having to just cheese the ai pathing. I love the world and 100%ed Skyrim, but I can’t get into Oblivion when the combat is this unfun. I’d like to do my next play through as a mage and understand the leveling system in Oblivion is janky. How can I play and still level up my character without it being a slog?