@Sundar 

Hello, Deco E4 does support both 2.4GHz and 5GHz, which can be found on the official website:

https://www.tp-link.com/home-networking/deco/deco-e4/#specifications

However, if the wireless speed is not as good as expected, let's try to check some basic settings:

1. What is the current network diagram/layout? How do you connect these 2 Deco E4s together, via Wi-Fi or Ethernet cable? Is the main Deco working as a router or access point? Generally, when Deco works with an existing router, it is suggested to turn off the router's Wi-Fi network and use Deco's Wi-Fi network instead to minimize the wireless interference.

Below are more details for your reference:

https://www.tp-link.com/support/faq/1432/
2. What is the distance between all the Deco E4 nodes? Is the 80Mbps the speed tested when connecting to the main Deco or the satellite? With your device connected to the 5GHz of the main Deco (you may temporarily disable the 2.4GHz network on the Deco app), please check the wireless link speed as the instruction below: 

https://www.tp-link.com/support/faq/2265/

Please connect your computer to the satellite deco and test the speed you can get from it and check the wired link speed as well.
Note: Please show us a screenshot of the speed test result.

If the wireless link speed is slow, try with another wireless device and confirm again, tell me the model number of the wireless adapters.

May it help~