yeah, pretty much any playstyle can be made OP in this game without mods. Sword/board is the default OP, easy mode throughout--mainly because you can be effective very early on. Shield bash is just too damn powerful. Going spells takes a while to get there, so it does maintain some much needed challenge in this game up to the mid-level play.
My first play through was sword and board. Second was spellcaster. I do like casters in various games, but I was just bored with it in Skyrim. Yes--to be efficient and effective for most of the playthrough you have to stick with that 2nd tier fire spell, I think, but that gets really boring. Even installing some "balanced" casting mods doesn't help all that much--it gives some diversity, but I find it just makes you even more OP.
3rd playthrough (more time than my second) is primarily dual wield. I find that it at least offers a little more challenge than sword and board because I am much easier to kill, but holy crap the dps!
I haven't spent much time modifying the skill tiers or leveling system because I'm worried about breaking various things, and I guess I have't been convinced of which one to try before loading a new game--this is something that I don't want to install in the middle of a playthrough, for reasons. The only mod I have installed similar to this is one that allows you to convert dragon souls to skills--like 5 or 10 souls per skill, something I find to be relatively balanced. I mean, pretty much anyone uses one shout 98% of the time and maybe one or two--at most--other shouts the other 2% of shout time. That's a shit load of dragon souls that never go used.