That rebuilding thing has never existed in Spanish football, and even less in Madrid or Barcelona. They are cheap excuses to justify failure.
Explain to the soci that this year does not count. You should demand, blame and point directly at the coach, veterans or president.
The president came 6 months ago and found the team in shambles, you can't blame him for anything since he can't just print money like Atletico, PSG or Chelsea do.
The coach has a part of the blame, still, he's lost some of his best players and wasn't given anyone on a similar level to work with, also the talk about his sacking is an overreaction when you just lost vs one of the best teams in the world but were missing Dest, Dembele, Fati, Agüero, even Braithwaite and also Alba wasn't fit to play, 6 players that could be starters and don't have reasonable depth options behind them.
The veterans are probably the main culprits remaining at the club that led us to this point, they're not at the level this club demands, they are also to blame for the weak training regime we've had for years but at least they cut their wages when they had no need to do so. With time, hopefully, they will fade out of the team, but yesterday they were needed just to fill the starting 11.
And the rebuilding part is nothing new for long time Barcelona fans and even less for Laporta, there was a rebuild period after Cruyff left, another after the Gaspart era (signing free agents, looking for gems on mid tier Ligue 1 teams, playing kids from youth ranks). Everyone knew Bartomeu was a cancer, there have been articles about how poorly our finances have been ran (signings and wages) so is it really that weird to think that after we got rid of that tumor, most fans don't expect the team to be somewhere near to the level it was from 2008 to 2019?
The current board don't need any excuse to justify failure because any non plastic Barcelona fan knew the reality we face. We've been criticized for years because we were wasteful on our signings and we closed the window with a 70M net gain and signed free agents, we've been laughed at for our wage structure and in one summer he offloaded the two juggernaut contracts we had, convinced some of our big earners to cut their wages by half and lowered the wage/revenue ratio from 110% to 70%. Under those circumstances and with a manager that they didn't choose but had to keep no one expects this team to win a title, getting out of groups and finishing 3rd/4th in the league are the expectatives, anything beyond that is welcomed.