And that right there is part of my problem. I don't mind if a pure theif/mage/fighter archetype is weaker or ineffecient than a multiclass character, but I *do* mind when the game bascially says "Pure Archetype becomes utterly useless after this point." And unless said point is fairly early in the game, it's usually too late to change styles. Really, when I've been happily whacking away at monsters for 25-30 levels, how do you think my conjuration/destruction stats are? Next-to-useless. If simply hacking away at enemies was a viable option for a good portion of the game, why should I bother expanding to other combat skills? I can't train them effeciently, since the game limits how many times you train per level, and getting any skill from 10 to 80 or 90 takes a looong time.
But this is taking the discussion off-track... max level allowed by the game is 255... of course, by that time, unless you've heavily invested in spells and game-breaking enchantments, you're gonna be running most of the time, and hope the guards can take care of the monsters.
Problem is that your max damage is limited, perfect amber sword with a shock damage sigil stone. At very high level the only effect is that both you and the enemies get more health, less of a problem with NPC but some monsters like goblin warlords and wraits end up with loads of hp at high levels.
Same basic rules in Morrowind and Daggerfall but their problem was lack of high level enemies.
And no the guards would not be able to handle the monsters, they are npc with low level equipment.
Would actually recommend to reduce difficulty if the enemies get to much health.
And yes it's hard to train new combat skills as they are weak compared to the old, only exception is bows to poison somebody at range, weakness spells to increace damage from enchanted weapons and summons as distraction.