I tend to agree. Though I wouldn't go as far as you would in saying M-U's were the be-all-and-end all, I do think M-U's had a very low survival probability at lower levels in AD&D, and were more powerful than the other classes at higher levels. Fighters, on the other hand, took a strong lead and weakened over time. Clerics and thief-types were more in the middle -- overall, clerics seem the most durable characters and got decent power at high levels.
Perhaps I only say that because my highest level character was a cleric . . .