Seriously speaking, the data center network architecture has developed from the traditional three-tier architecture to a two-tier flat architecture, and the technical path is correct, which has brought many performance and management benefits on the two-tier architecture. I think you've heard enough about it.
However, faced with the new requirements of data center access layer, especially when deploying the same VLAN virtual function in the network, network providers often push the architecture to the extreme, for example, Cisco's DFA technology. The only thing they do is to treat my network as a big switch, and then you connect this port, random Vlan, arbitrary deployment of virtual machines, and arbitrary expansion of the second layer.
However, manufacturers have misjudged the demand, the market is not ready, and customers have not bought it yet. You can see how many customers are using it now.
As for the shortcomings, immature technology is one aspect. I think the problem is that the essence of the customer's business model has not changed. Originally divided into business areas, it is now deployed on Juniper's VC or Cisco's 7-5-2. The service is still sub-regional, but the location of the server gateway has changed, that's all. Therefore, the essence of change is the change of business model. Good technology is also a pile of scrap iron without the support of the corresponding business model …
Of course, the high cost of reform should also be one of its disadvantages.
Finally, in theory, every current architecture is an upgrade of the last one, so the last one should have more advantages, but it takes time to change people's popularity.