Heading into Tuesday's second leg at Anfield 3-0 up, the Spanish champions were powerless to stop Jurgen Klopp's side as they ran out 4-0 winners on the night to book their place in the European showpiece in Madrid on June 1.
The match marked the first time Coutinho had returned to Merseyside since leaving the Reds for Camp Nou in January 2018, but he struggled to make an impact on the game and was replaced after 60 minutes by Nelson Semedo.
Brazil international Coutinho has struggled to hit top form for much of the campaign, and Capello was less than impressed by his failure to show up in such a big game while questioning why Ernesto Valverde selected him in the first place.
"Valverde was a bit presumptuous in playing the same team from the first leg," he said while working as a pundit for Sky Sport Italia. "For me, Coutinho didn’t have to play. He does nothing away from home."
Coutinho's failure to live up to his £105 million ($135m) transfer fee since arriving in Catalunya has led many to believe that he could be on his way out of the club this summer.
Manchester United and Paris Saint-Germain have both been mooted as possible destinations, though Goal understands the player himself is keen to remain with the Liga giants.
The club's hierarchy are still to make a final decision on his future, though it is understood that some improved performances in recent weeks have led to them leaning towards retaining the former Inter playmaker.
As for Barcelona themselves, their dreams of a first Champions League title since 2015 are over, and with the Liga title already secured, all that is left for them to play for is the Copa del Rey, where they will face Valencia in the final.
And Capello believes that their failure will have been greeted as warmly in Madrid as it was in Liverpool, with fans of his former club, Real, happy that their great rivals would not be winning the continent's biggest trophy in their home city.
"Barcelona found themselves three times in front of Alisson, who made incredible saves, but showed concentration problems as in the fourth goal [scored by Divock Origi]," the ex-England manager said of Barca's performance.
“They can’t mess up the way they did because Liverpool’s players are at such a high level that they punish you.
“Liverpool, Anfield but also Madrid exploded. It would’ve been worse for them in Madrid if Barcelona won the Champions League there."
Barcelona will return to action on Sunday when they look to dent the Champions League hopes of minnows Getafe, who currently sit fourth in the Liga table with two matches to play.