It was a piss weak league and cup teams back then. Europe was really shit, Barca, Milan, Madrid all shit. No Ronaldo or Messi around.
It was extremely competitive, and not remotely weak. In domestic competions, Arsenal pushed United all the way, and it's not so far-fetched to suggest that, had Arsenal won the FA Cup semi-final, they would have had the momentum to win the league as well (so, just how important was that Schmeichel penalty save?).
Juventus were a great side and very highly regarded, and United produced a stunning comeback against them to even reach the Champions League final. Bayern were strong too, and they had the benefit of playing in the final against a United side seriously weakened by suspensions (under current rules, both Keane and Scholes would have been available for the final).
Looking back on that year there were so many incredible games that went United's way, but could easily have ended differently. United didn't stroll to the treble because they were obviously the best team, they fought and scrapped their way to it because they were a great team (or should that be TEAM). There is much to admire, though I'm loathe to admit it, about the current Liverpool side. They also appear to be a great TEAM.