The thing that make the treble so impressive for me was how tough each competition was.
The league was very competitive. As well as us, Arsenal & Chelsea had excellent teams, Villa had a great season and were top of the table til about Xmas, Leeds has just assembled that decent side with Hasselbank finishing top scorer & West Ham had one of their best ever seasons too. Liverpool only finished 7th that year despite having Owen & Fowler up front who bagged 32 goals between them.
We had a hell of a tough run in the FA Cup. 5 of our 6 opponents were Premier League opponents, including the 2nd and 3rd placed teams in the league. Even the one lower league team we faced, Fulham, were half decent, winning Division 1 with over 100 points that year. Compare that to the almost embarrassing run we had in 15-16, its night and day.
We also faced some really tough teams in Europe - Bayern, Barca, Inter, Juve then Bayern again. That's way tougher than, say, 07-08 when we didn't face a really difficult opponent til the semi final stage.
Its possible to get quite far in a competition with a few lucky draws or through your opponents in the league disintegrating, but we had about the toughest possible route in all three that we won.