Because you have essentially dropped an attacker for a centre back and we already don't score enough goals.
Plus, it's essentially 5-4-1 however you want to frame it.
Based on "player profiles" position-wise it would be, but that's also a bit too simplistically put.
In the case of Lisandro and Yoro I think it could be too CB-y in the centerback to have a strong counterargument, but still the change in responsibility and roles does make it quite different from just 5 at the back or simply adding an extra centerback.
It does also depend on who you put in the wingback-positions, as it's quite different to have, say, AWB and Malacia in wingback positions, compared to:
- Frimpong/Grimaldo (Leverkusen's style with them being very direct additional forces in goals and assists);
- Bernardo/Grealish (like two seasons ago at City with two playmakers with stamina);
- Moses/Alonso (Conte's Chelsea and them pretty much being on the sides to cover a lot of space, with the stamina and just enough technical abilities to get a lot of profit out of the space afforded to them by opponents focusing on Hazard and such - basically the first prototype of the modern 3/5 at the back systems, but an approach that has become more out-of-touch with the more holistic/all round styles in the current era of football, with perhaps Frimpong and Grimaldo coming closest in their "classic" attacking wingback roles, but their speed or technical abilities being quite a bit beyond these more "base" versions)
- Llorente/Lino (a box2box/hole player midfielder and a winger in a more asymmetrical style like Atletico's current setup).
But also even compared to Mazraoui and Shaw. They are both more used to a fullback position, but Mazraoui used to be a midfielder and Shaw has also grown into more of a playmaking fullback over the years, making them more of a hybrid option at the wingback in case the strategies would move in that direction.
Based on ETH's general approach I think he will stick to the space for Mazraoui, Dalot and Shaw being inverted fullbacks. But as an option here, especially if Yoro and Lisandro (or even Shaw at LCB?) show comfort and covering more space on the sides rather than focusing on the center, I think it would really fit better to call it a 3-4-3 or 3-5-2 rather than a 5-4-1.
The reason something like this worked more as a 3-4-2-1 at Leverkusen for instance, is when Stanisic played RCB to Frimpong's RWB is that depending on the run of play, Stanisic was basically RB with Frimpong moving more towards either RW or even AM/SS. If it were 5-2-2-1 Frimpong would be running up and down the wing and do much more defensive work than his usual role entails. That makes it different from how you could just add Maguire or De Ligt at the end to defend the lead or against crosses, etc, and it's basically just stacking the defense more. But based on some of his earlier work - as starting XIs - I'd see ETH turning the wingbacks into something either more offensive or midfielder-like in case he opts for such a setup. His latest seasons at Ajax basically were that, actually, and even with Mazraoui and Lisandro taking on those very roles.
As - on paper - Alvarez was DM, Mazraoui was RB and Blind LB, but in practice it was much closer to a 3-4-3 with Mazaoui and Blind acting way more as (offensive/side) midfielders than as fullbacks, except for possible under-pressure moments, and with Alvarez being the physical force between the more creative Timber and Licha, who joined midfield very often. I guess that means that if Yoro can do a Timber-like (or Azpilicueta, Ake, Gvardiol, Walker, Reinildo, Hermoso, etc etc) job, than a 3-4-3/3-5-2/etc could be an (offensively apt) option for us. Because I think you'd be better of playing Mazraoui RCB than Maguire or De Ligt if you want the team to be able to build up and be a threat offensively and such, instead of just being a fancy renaming of a 5-4-1, like you said.
But it could be an idea, especially if neither Casemiro nor Ugarte get things ticking, to move responsibilities in control and build up to another system. Again, if Yoro works as RCB as well, I could see something like the following setup working for us:
Onana | | |
Yoro
(Mazraoui)
Lindelof | De Ligt
Maguire
Evans | Licha
(Shaw)
(Lindelof)
(Malacia) |
Ugarte
Casemiro
Collyer | Mainoo
Eriksen
Gore | |
Mazraoui
Dalot
(Amad)
(Antony)
(Bruno) | Shaw
(Dalot)
Malacia
Antony
(Mount) | |
Bruno
Amad
Mount | | |
Hojlund
Garnacho | Zirkzee
Rashford | |
Or some variation of this (though I can imagine the second/alternative choices being question marks at wingbacks in case less than two of Dalot/Shaw/Mazraoui wouldn't play there)