"That's life," McCullum told Sky Sports after England's nine-wicket defeat. "We obviously coughed up the opportunity to win the series. We did some good stuff throughout, and we leave ultimately disappointed, but also very much complimentary of how Pakistan played. But we know within ourselves that we've had an opportunity to have been better than that and we're a little bit disappointed about that.

"Credit to Pakistan, the way that those two spinners bowled was superb," McCullum said, after Noman and Sajid had combined to rout England for 112 in their second innings in Rawalpindi.

"I thought they varied the pace beautifully. Noman from one end, taking pace off most of the time with the occasional fast one, and Sajid flipping that around and putting pace on with the occasional slow one. I thought was great partnership bowling. And our guys weren't able to sustain the pressure, unfortunately."

Asked if he was comfortable with the extreme measures that Pakistan had taken to bring their spinners into the series, including the seemingly unprecedented reuse of the first-Test pitch in Multan, and the raking of the Rawalpindi surface to exacerbate the turn on offer, McCullum said he welcomed the initiative they had shown.

"I kind of like it to be honest," he said. "They were brave enough to make decisions on their personnel, and they were brave enough to make decisions on the surfaces that they wanted to play on.

"When teams come to England, ideally we play on the surfaces that we're more accustomed to, which allow our strengths to really flourish and maybe paper over some of the weaknesses as well, which every team naturally has.

"I'm a little bit surprised it's taken Pakistan as long as it has. Because when you go to Sri Lanka, India, Bangladesh, the ball is always going to turn. What we had here a couple of years ago, or in that first Test match, where it was pretty flat, was a different challenge. It'll be interesting to see over the next couple of years whether they persist with these types of services, but certainly there are no excuses from our point of view. We had our chances, and we ran second."

Despite remaining magnanimous, McCullum acknowledged that the series defeat would increase the scrutiny on his team. Ollie Pope and Zak Crawley were notably short of answers in the more extreme conditions, while Brook managed a top score of 26 in his final four innings of the tour, having racked up four centuries and a fifty in his previous six in the country.

"It's pretty much the same batting group that came here two years ago, and were outstanding in these conditions, and it's the same batting group that put on 800 in the first Test match," McCullum said. "As the conditions changed, we were presented with different challenges and we weren't quite able to adapt to those challenges. And that's a missed opportunity."

"I have no doubt, and the skipper has no doubt, that our batting group that we've now had together for the best part of 18 months is the best that we've got," he added. "We're very confident, we've just got to make sure we keep allowing guys to develop them and keep becoming the players that they want to become, and will benefit from that."

The focus will also fall on England's spinners, particularly Shoaib Bashir and Jack Leach, whose direct counterparts Sajid and Noman exploited the conditions with significantly more success in the final two Tests. Bashir, whose selection for the India tour had been on the basis of his natural attributes, rather than any proven record in first-class cricket, has now bowled more overs in 2024 than any other player, but his series haul of nine wickets at 49.66 pales compared to Sajid's 19 at 21.10.

"[Sajid and Noman] were brilliant in the way they bowled together, and they challenged in different methods with the paces that they used," McCullum said. "Could we have been better? Yeah, of course, right? Anytime you lose a Test or lose a series, you've got to have that period of reflection. And we'll do that, and say, right, next time we're presented with conditions similar to that, how will we respond? What do we need to do? Do we need to vary our pace more? Do we need to adjust our tactics more? That's natural, right? It's no difference to when a batsman gets out."

"You're always trying to improve, but you've got to be really careful that you're not seeking perfection, because it doesn't exist in an inconsistent game. The game we play is going to come with periods where it's not going how you want it to, but you've still got to hold firm.

"We will be confronted with spinning conditions at some stage in the future, and we hope that some of the lessons, good and bad that we've had throughout this series, will give us a bit more of, a bit more of a base to be able to be successful."