"Due to the limitations in the number of enemies in the Single Player Campaign and the fact that enemies do not ever respawn, it is impossible for a player to achieve any of the last titles.."
This is in fact quite untrue.
There are an unlimited number of enimies in the Single Player Campaign, at several junctures:
Enemies do not ever respawn, HOWEVER, they can be summoned...
In the first part, summoners summon, and charge limiting their effectiveness,
in the ice caverns, the summoners do not move, intending to target one individual in the party,
in the swamp, and the maze beside the swamp, the summoners do not move.
while a dedicated party member can heal him, if he keeps the summoner OUT of attack range,
Then there are an unlimited number of summoned enimies, not spawned...
Which yeilds both an impressive amount of gold, 9,999,999 and an unlimited amount of both unique,
and special artifacts, usefull in one way... increasing mana, and freezing enimamies.
RIght now, I have a troupe of 7 full Arch templars of lvl 70... Shall I provide a screen shot of said party?
Well that require's more grinding than I'd expect.
BUT, if you check in the game code, you'll find that summoners actually have a limited number of times that they can summon mobs. After something like the 100th or so summon, their AI changes and they just rush in with their standard attack, be it a melee or ranged or magic attack.
Also consider the fact that levelling skills is an exponential xp grind. The difference between level 70 - 71 is minimal compared to level 95 - 100.
I would still be very surprised if this was possible to get to level 100.