Make no mistake - England's Ashes defeat is bad. Very bad. Of all of the trips to Australia I have witnessed, this is the most disappointing. England are not a terrible team. They have had fleeting chances to get on top and beat Australia. But, through a lot of their own making, they are 3-0 down. That is hugely frustrating.

England's poor performance simply has to come back to their preparations because, through choosing not to play any proper warm-up matches, they did not give themselves the best chance. Coach Brendon McCullum has now admitted that was a mistake, and for him to say that is a massive step forward. Imagine how much it must hurt him to say he was wrong after all the talk. If he had stubbornly stuck to his guns, as this England hierarchy has done before, I and many others would have been wondering if he should still be in the job. It was so obviously not right.

That he has not gives me hope that there can be a future for McCullum and Ben Stokes in charge of England's Test team. Stokes' answers in his press conference suggested he is resolute in wanting to continue. He was always going to say that in the middle of a series but, if he feels able to, that is the right decision. England remain a better-led outfit when Stokes plays. I looked in his eyes today and he is hurting, upset and angry. Because he is the heartbeat of the team and a massive part of the dressing room, it would be a huge ask for someone else to take on the side with Stokes in the ranks. And it is not clear who that person would be, especially because vice-captain Harry Brook has shown a lack of maturity.

It was certainly England's best performance of the series in Adelaide, so - assuming things do not go badly wrong in Melbourne and Sydney - Stokes should continue if he feels his body can still stand up to playing Test cricket.

As I spoke to Brendon on the outfield, I did wonder if he may have been talking to more than just me. It felt like a message to his employers because he, and everyone else involved in the decision-making, will have to give an account to those in charge at the England and Wales Cricket Board after this tour. A response lacking in accountability may not have washed.

If McCullum, who is also scheduled to lead England at a T20 World Cup in February, is serious about reviewing what has gone wrong and accepting there have been mistakes, then those two can go forwards together as a partnership. Right now, that leaves managing director Rob Key looking the most vulnerable, simply because he is the easiest for the bosses - ultimately ECB chief executive Richard Gould and chair Richard Thompson - to get rid of.

I do think as a trio they are far too similar. When England have been at their best, they have had opposing characters like Michael Vaughan as captain and coach Duncan Fletcher in 2005, or the stern Eoin Morgan and relaxed Trevor Bayliss, who won the 2019 World Cup. Key is a lovely fellow but he might consider whether he has let McCullum and Stokes have too much of what they want. Stokes is a great on-field captain and McCullum has a terrific attitude as coach, but they needed to be steered in the right direction when it comes to preparation and planning.

Instead of challenging that, being someone to will keep Stokes and McCullum's feet to the fire, Key signed it off. There needs to be someone with a more old-school mindset to challenge ideas and keep an eye on the change, with Alec Stewart one very obvious candidate after all the fine work he has done at Surrey.

England have decent players like Zak Crawley, who played beautifully in scoring 85 yesterday after struggling for two Tests, or Jamie Smith. Yes, he played a poor shot on Sunday but he made a really nice 60 in the second innings, having struggled so badly beforehand. That simply goes back to the preparation.

I said half-jokingly after the second Test in Brisbane that England would play well now in Adelaide because they had had their two warm-ups. Had they batted like they did here from their position of strength in the second innings on day two of the series in Perth, they'd have won and we could be looking at a very different situation.

And if Stokes and McCullum are in as reflective mood as it appears, they must also consider the environment in their own dressing room. We do not get to sit in the dressing room so never truly know what goes on, but do players feel able to speak up? Is anyone able to go against the model?

Three England players arrived for the day-night Test in Brisbane having never played a match against a pink ball. It would be a much healthier environment if they could say they wanted to go and play in the match in Canberra to prepare. There needs to be debate and discussion within a dressing room, and healthy competition, as much as McCullum likes to talk about alleviating pressure.

Bazball as we knew it is in the skip. That has gone. But I have been encouraged by the words - as well as by how Crawley batted on Saturday and Brook in the first innings. If this is the start of a more mature and considered tempo, backed up by change off the field, then there can be a future.

Jonathan Agnew was speaking to BBC Sport's Matthew Henry.