Behind runaway race winner Max Verstappen, Lewis Hamilton led team-mate George Russell to bag a double podium for Mercedes to jump Aston Martin in the constructors' standings. This came as Stroll classified in sixth ahead of home favourite Fernando Alonso in seventh.
Since the AMR23 has often been the second-quickest machine behind the Red Bull RB19 throughout the early races this season, the Silverstone squad was surprised to find itself adrift of the "rocket ship" Silver Arrows while also struggling to better Ferrari's pace.
Stroll said: "[Mercedes] had a rocket ship. I'm not sure where they found that pace.
"I was expecting us to be the strongest car after Red Bull. I expected that after all the races this year. We just didn't have it.
"[We had] a lot of degradation and [were] struggling with our pace compared to Merc, Ferrari. Red Bull is in another league. We just didn't have the upper hand."
While the removal of the final chicane in Barcelona was well-received by drivers, it did take away a slow-speed section and major acceleration zone - areas where the AMR23 has excelled.
Also, with the faster final corner increasing speeds onto the main straight, Aston Martin was also towards the lower reaches of the speed traps with its package that has at times proved draggy.
However, Stroll placed the blame for the competitive slip compared to Mercedes squarely on the management of the Pirelli tyres.
Asked for an explanation of the problems, he said: "Just deg. [Mercedes] just looked after their tyres really well.
"It felt like at the beginning of the first stint, when we were in third [after passing Hamilton on lap one while third-starting Lando Norris dropped after contact], I was comfortably just keeping that gap to Carlos [Sainz, Ferrari], even pulling away from Lewis a little bit.
"But then, like five laps into the race, they just didn't have any deg and I just felt the tyres dropping off.
"They were pushing on. Even looking at Russell's race, I think they were able to do that all race. They seemed to have a really good car today."
Aston Martin's race was also notable for Alonso radioing the team to say he would not attempt to battle Stroll as he closed on his stablemate in the final laps.
Stroll reckoned this was indicative of Alonso playing a team game. the Canadian said: "We were sixth and seventh - bringing the car home, thinking about the constructors' championship.
"We respect each other as team-mates and we want to score as many points as possible for the team.
"In those situations, it sucks to have an accident over small-ish points.
"It's more about bringing the car back in one piece. All the guys that work super hard at the factory deserve that."
