England captain Alastair Cook said his side remained "a work in progress" after a 10-wicket defeat by Pakistan at The Oval tied the Test series at 2-2.
Cook's team stood a chance of returning to number one in the Test rankings with victory but lost on the fourth day.
"For a batter, our currency is runs - and as a top order, we haven't consistently been doing it," Cook said.
"We played at a disappointing level as a side and we weren't good enough in all three areas of the game."
England went into the final home Test of the summer needing to avoid defeat to hold trophies against all nine Test opponents for the first time.
"We're still the same side who beat Australia and won away in South Africa, so it's not all doom and gloom, but we're a work in progress," Cook added. "We had the opportunity to beat Pakistan and it's frustrating."
Three dropped catches by Cook's team on day two allowed Pakistan to add a further 120 as the tourists eventually compiled 542, veteran Younus Khan making 218.
The skipper also put down a chance on day three, and he said of the fielding blemishes: "The catching is a concern: when we've won games we've caught our catches; when we've lost we've dropped our catches.
"We've definitely dropped in standard this series.
"You expect to win your home series, but Pakistan showed their class - we knew Younus was going to get us eventually as you don't average 50 in more than 100 Tests if you're not a class player."
England passed 400 only twice in the series and were bowled out for under 300 on four occasions.
Cook and star batsman Joe Root finished with 935 runs between them at an average of 66.78 but the other members of the top five - Alex Hales, James Vince and Gary Ballance - could only muster a combined 498 at an average of 22.63.
Asked what had disappointed him about the series, England coach Trevor Bayliss said: "It is the same as for the last six to 12 months - we rely very heavily on Cook and Root to score runs.
"Jonny Bairstow has done extremely well and Moeen Ali has made some runs but we need two or three other guys to stand up in the batting order."
A 'special' time for Pakistan
Pakistan captain Misbah-ul-Haq, who scored a century at Lord's and half-centuries at Old Trafford and Edgbaston, was named man of the series for his team.
"The win was special, keeping in mind it was Independence Day," Misbah told BBC Test Match Special.
"It was something special to draw the series here after being 2-1 down, losing the second Test badly and losing the third. But the way the team fought back, I'm a really happy captain."
Pakistan have two one-day internationals against Ireland followed by five ODIs and a Twenty20 against England, before another away tour - of New Zealand and Australia starting in November.
"In Asia, this team's unbeatable as our spinners come into it more and our batters are better," Pakistan coach Mickey Arthur said.
"It's the games away from home which will determine how far this team can go. We've got a tough itinerary now."