UPDATED Major Skills Tier List | Oblivion Remastered
S - Alchemy, Destruction, Restoration
A - Heavy Armor, Block, Armorer, Blade, Blunt
B - Alteration, Conjuration, Athletics, Light Armor, Sneak, Marksman
C - Illusion, Acrobatics, Mysticism, Mercantile
F - Hand to Hand, Security, Speechcraft
I haven't tested Marksman or Hand to Hand, so maybe they will change later, but I'm fairly certain they won't move.