It seems every class that I try, if I make it to the higher levels without restarting, I am OP despite the effort not to be. However, if I don't improve weapons and armor for example, the lower levels are too hard. Any tips? I am interested in advice for all types of characters.

Master difficulty with simple scaled armor and Unarmed fighting. I don't use shouts or powers except Restoration and potions.
Lightly armored and even lightly armed.

I use bows ONLY when necessary.

Uh huh. Sure you do.

I don't have a reason to be lying. Its doable. Alibi my Restoration if the first skill at 100 next to Sneak and Light Armor. Easily go broke just from potions in the first levels....

The problem is that enemies scale only up to the high forties/low fifties. After that, they stop levelling up when you do.

Turn up the difficulty and start using less-effective weapons/armor once you hit that point. Or get mods.

Make your own weapons and armor. That helps for a while.

Use iron / steel weapons, and upgrade them. You'll be strong early on but not a dervish of destruction at level 25+.

I generally use weaker armor and weapons if I prefer the way they look over top tier stuff.

That sounds like quite the challenge. Is it more tedious than fun, though?

Yeah, my warrior wears ancient nord and uses draugr weapons because they look the best to me. I don't care for daedric or ebony or all that. Dwemer looks awesome though.

In the beginning its extremely difficult. But once you start leveling out with your enemies its easier. My method takes patience to play as so some people probably would say it isn't fun.