I think the idea was that each faction is vastly different so that they didn't feel samey. The argument is "well people will just pick soviets because it's the most viable/less gimmicky then.", well people do that anyways because soviets still have tools and a good tech structure vs USF. If you pick USF now you are basically picking them for the crew repairs and a few outlying strategies which can be similar to soviets.
Ignoring top end play, factions are pretty samey with USF/Brit/Soviet skins thrown onto them.
As far as that playstyle being bad for the game, I look at fighting games and each character is an arch-type that plays differently. So if I'm a zoner and I'm up against a rushdown character, I need to be even more cautious then I normally am about defense. In this context it seems like every faction is a Ryu/Shoto clones with slightly different things. So people just pick Akuma because he has a gross kit compared to Ryu.
I think "healthy for the game" is up to personal opinion because at that point what is? Would come down to the underlying vision of the game that I don't think had ever been openly discussed.
I keep seeing this 'every faction is the same' argument, but I'm not really buying it. Riflemen and Conscripts play nothing alike, USF LV pressure is decidedly different in role and timing from a T-70. Lategame is night and day, with the decisive push of USF infantry and TDs style contrasting with the slow manpower grind of Soviets hidden behind a million mines, sandbags, 6 man setup teams, and rocket arty.
My problem is that people seem to define factions having the tools needed to play the game as turning everything into the same faction. But the game requires that you have that toolset to work within its framework. Every faction needs some form of suppression to control blobs, AT Guns and snares to control vehicle pressure, Artillery to break setup team and emplacement spam, Vehicles, and a variety of specific counters to things like Mines and Snipers.
It makes far more sense to me to define asymmetry around faction specific mechanics (OKW Trucks, vet 5, and Salvage, Soviet 6 man teams and merge, etc) or equally strong, but different weapons (50 cal vs MG42) that fill the same role rather than trying to compensate for missing tools with broken units. (Brits..)
The expansion armies all started out as an attempt to do the latter, and while you can do this to a limited extent, (Ex: USF having lots of Zooks to compensate for AT Gun on only one side of tech tree) it tends to make the factions increasingly one dimensional in how they play. (I don't entirely agree that USF has to win in 15 mins or less, but going LT in 1v1 you *need* to do damage to be in the game late)
The end result though was they were unable to make the game work this way. OKW was more or less completely walked back and turned into a more traditional army, while USF is close to one while missing a few tools, and Brits remain the big outlier.
The TL;DR: version is that I agree the lack of toolkit is the problem here, but I don't think any of the Allied factions play in a similar manner, and any further patches should focus on adding more tools to their stock rosters while further emphasizing their different factional traits.