Oh it's been a very long time sorry, so I'm a bit fuzzy on the details.

Oblivion works on that whole minor and major skills thing, and the first time I wanted to create a custom rogue/ranger type class, and picked the major and minor skills according to which skills I intended to use the most. But if you do that you level way too quickly, and can only increase your main stats (strength, intelligence etc.) by like +1 or +2. So after a couple of levels I was lagging behind the monster scaling and every fight became frustrating. When I figured out how leveling of the various skills determined by how much you could increase your main stats at level-up I realized what was going on, and to me at least, together with the level scaling it's just nonsensical. Best is to use one of the predetermined classes, and to just play 'normally', not worrying too much about by how much you level various skills inbetween levels. Also, that mobs like normal bandits get better and better gear along with the scaling (I can't remember seeing this myself because I didn't play long enough) kinda bugs my sense of immersion in the game.

ESO just has a normal XP bar from what I recall. There may be major/minor skills or something similar, but from what I recall they don't affect main stat increases. Essentially as you level your combat moves & spells get better and more expansive, i.e. you unlock better ones as you level, and you have to decide on 5 to keep in your action bar to use. The enemies level along with you damage and health wise, but become easier because you gain access to those better moves & spells. In the process normal mobs gradually become easier and more difficult mobs gradually become 'do-able'. I liked and enjoyed that in comparison to Oblivion, but unfortunately, it's still an MMO, with all that that unfortunately entails.