I think those comments were taken fairly out of context. Of course you play differently with different players, and he's always done so.
At Utrecht he often played a type of dynamic diamond midfield, which he adapted to the opponent, like when they almost knocked out Zenith (which was quite a feat at the time when comparing the players' levels) in the Europa playoffs.
Then after some tweaking (and a difficult/struggling) half year at Ajax his first full season was the one where they had their most legendary season with Frenkie, De Ligt, Ziyech and Tadic, etc. But after a year that was a little less fluid, the two seasons after that had a new foundation, where instead of Frenkies, you had a Gravenberchs, instead of Tadic false 9 you had Haller and instead of the playmaker RW Ziyech, you had Antony. Instead of two playmakers in DM/CM (Frenkie + Schøne) and one hole player/finisher midfielder (Donny), you had one holder helping a shorter but more technical, fast and agile CB duo in Alvarez, having Gravenberch and Berghuis around him to do more of the playmaking.
Both had a lot of possession focus, but played very differently.
The plan seemed to be to get Frenkie last year, but even then it would be very different. Bruno can finish, but he's not like Donny, and Casemiro is obviously better than Schøne, but Schøne was a real playmaker. So even with the super carrier, the midfield dynamic would be very different, and Bruno wouldn't suddenly be a tiki-taka guy who isn't addicted to the killer pass.
In a way it seems a little between the two Ajax sides he built, in design. The midfield is relatively close to his early Ajax, while the attack looks more like the later Ajax. I feel like the lack of playmakers is what causes the biggest difference. Take out Eriksen, and you have to hope Bruno is disciplined enough (in keeping composure) and Mount is calm enough. In that sense. That's very different from having Tadic, Frenkie, Schøne and Ziyech all in one setup, with someone like Blind in CB to add an extra dimension with his passing, and with Donny and Neres having their occasional moments of playmaking. It's also very different from having Gravenberch, Berghuis and Tadic, while also having an extremely dynamic backline in Blind, Licha, Timber and Mazraoui all having either playmaking or carrying skills, leaving a lot of room to use whatever space is there.
Now Shaw and Licha are under contract and are capable when in form and fit, AWB is growing at it. Eriksen can do his part, I guess they're hoping Mount will adapt to the part as well. Sancho seemed like a perfect part to this, but after so many months, and now this, it seems a lost hope. Casemiro can be all right in his passing, but when he's not in form it's getting clear the base line in his playmaking is pretty low. Bruno can do great things, but he's also a huge Bruno. Rashford can do some things, but if the play isn't ticking behind him, he will not carry the team. Last year the midfield was more solid, which led to Rashford having more physical and mental space to do what he's good at. A few years ago I thought he'd develop some more playmaking skills too, but I'm beginning to think that he will be a player great at doing his part. I think they were hoping that Hojlund could be something more between Tadic and Haller in type. At least when I watched videos, he did seem to play along pretty well.
So now it just kind of looks like some key foundation is missing to come close to those Ajaxes. And ETH is right that the injuries really do not help, but I think instead the squad building was not balanced enough. Now most backups can do a part, but if the whole back line is just doing a part, you miss 4 key assets. If the foundation is there you won't lose with an Evans or Maguire at CB filling in, or even with Lindelof doing a part at LB. But now the whole backline feels like a Lindelof playing LB. I'm not sure if I have faith in Mount, but I think it's too early to decide if he can or cannot adapt to the system of this team, even as an 8.
So even if ETH made a lot of mistakes, I don't think it's right to judge him too much just yet. I don't know enough about the Sancho situation, but with other players back they can start to build more on stronger foundations, but it does seem like it's even more urgent to fix the backups. You don't need to get rid of everyone, but you don't want to lose your entire backbone if Licha and Shaw are out. Defense doesn't score goals, but losing two playmaking elements, especially with midfields like we see nowadays, seems like a lot to me. Let alone if your entire front 3 aren't really playmakers either, nor is your leader in midfield. With such players back, even if Mount never amounts to bigger things, his worst will be less bad if he is aided by players who can take on more responsibilities in possession.
I'd understand if the ties tear, and maybe this squad and club doesn't fit with ETH. But I do feel like it'd be worth it to leave things as they are for now. But I hope the next injury wave won't create a similar assembly of parts in the weekly XI. The more I think about it the less it surprises me that there's no visible structure at the moment and that it feels like it's a lot of hoping for the best. Honestly, if your XI looks like this – and it might be a bad idea in the long run – it could be an idea to just grind it out like the Simeone Atleti 4-4-2 from the 2010s. It won't look pretty, but it would be a system that would cost you less if you have to build around McTs and even Brunos.
(obv I'm biased on many points so don't listen to anything I say pls)