The two-time champion ran to ninth on Saturday, lapping 0.939 seconds slower than polesitter Max Verstappen. Team-mate Lance Stroll, meanwhile, clocked 12th position.
That marked the worst qualifying result of the season for Alonso, who notably was second quickest over a flying lap in Saudi Arabia, Miami, Monaco and Canada.
He reckoned Aston Martin had virtually achieved its maximum at Silverstone, conceding it was impossible to see how the team could have climbed higher than the top eight.
This performance meant the team needed to diagnose why the similar characteristics of Barcelona, the Red Bull Ring and Silverstone had disrupted the form of the AMR23.
Alonso, who scrapped into Q2 by 0.02s owing to late track evolution in a drying session, said: "Obviously, I'm never satisfied with between P9 and P12. I think it was not the strongest qualifying for the team so far but difficult to see where we can do a little bit better.
"Maybe 0.1s, 0.15s. But more than P8 or something like that, it was impossible.
"We need to keep working, understanding, a few qualifying [sessions] already on circuits that we were not competitive.
"Barcelona, Austria and Silverstone - all three of them seem a little bit similar in a way in track characteristics. So, we need to understand that."
McLaren, which Alonso reckoned had been "so-so" in 2022, was the surprise package in qualifying.
Lando Norris ran to second place ahead of team-mate Oscar Piastri to replace usual contenders Ferrari, Mercedes and Aston Martin as the next-fastest behind Red Bull.
With Aston Martin falling behind the Woking squad, Alonso said his team needed to make it through the Hungary-Belgium double-header later this month before resetting over the summer break.
"They've been very fast," Alonso said of McLaren. "They deserve the position they are in. It's not like a casualty. They've been fast and improving. So, I'm happy for them.
"Especially after a few races, I think McLaren was very fast last year in Austria and Silverstone. They were so-so in the championship and this year they are also fast in certain circuits.
"So again, I think we need to go through Budapest and Spa and make a reset after that and see where we are."
