In early 2000s, we had:
1997-2000: Van Gaal, sacked because he moved somewhat from Barca DNA. Won 2 La Ligas in 3 years, but it was not enough.
-- finished 1st, 1st and 2nd (5 points behind Deportivo)
2000/01: Hired Serra Ferrer. Sacked in April when we were 5th and 17 points behind Real Madrid.
2000/01: Hired Carles Rexach. He managed to reach the 4th place in the last few rounds, due to Rivaldo's magical scissorskick against Valencia for 3:2 in the 90th minute of the last round of a season.
2001/02: Rexach ended 4th in La Liga, lost against RM in a Champions league, lost against Figueres in Copa del Rey and lost to Balaguer in the Copa Catalunya. He was sacked, we re-hired Van Gaal whom we sacked in the first place in 2000.
2002/03: Van Gaal now got rid of Rivaldo and we remained without star players (except so-so Kluivert and Saviola).
Van Gaal had only 6 wins in the opening 16 rounds of 2002/03 and left in January.
We hired caretaker Antic. Barca recovered slightly from Van Gaal's horrible start, but we ended 6th, barely qualifying for Uefa cup, 1 point infront of Bilbao and 2 points infront of Betis, winning only 56 points. We were 22 points behind RM.
2003/04: then we hired Rijkaard.
My point, let's say that sacking Van Gaal was something like sacking Valverde.
Van Gaal won 2 titles in 3 seasons, EV won 2 in 2.
After sacking Van Gaal, we had 3 horrible seasons and a first half of 2003/04 when even Rijkaard was almost sacked.
So, we sucked for 3 and a half years.
Currently, since sacking EV, it passed only a year and a half.
So, if we want to compare it with the past, there is still a lot more room for a freefall and sinking deeper.
Also, since EV, we sacked only 2 coaches.
In 2000s after sacking Van Gaal, we sacked: Ferrer, Rexach, Van Gaal in the 2nd stint and Antic.
Judging by the 2000s, we still need to sack at least 2 coaches before seeing some improvements.
But, the bad thing is back then we had money and we bought Ronaldinho who changed our fortunes.