My few cents on the topics of this thread.

This is what I can see was discussed.

Feature request 1: Set the linked Deco that satellite Deco connects to.

This feature is under Deco software developers control. If people keep asking, they can implement it. This is especially useful for a mesh with Deco nodes in close proximity of each other.

Feature request 2: Set the linked Deco that a device connects to, or a preferred one.

This feature is not under Deco software developers control. It is device that goes "I need to connect to WiFi, I know the network SSID and password, WiFi network presents me with multiple nodes, that will be the node I will connect to - my decision."

That is what Deco support may be struggling to explain. Disabling "Mesh" in Deco node for a device does not glue device to that Deco node. It is just Deco node stops saying to device "look, there is another node you may wish to connect to, perhaps better. What do you think?" 

Instead, Deco node accepts connection from that device and that's it. If device decided to switch to different node, on its own, Deco node can do nothing about it.

The only way I could think how Deco developers could implement it is make each Deco node create its own WiFi network with own SSID. We have Main and Guest networks, that could be Node network in addition to them. Each Deco node allows to set its own Node specific SSID/password, and devices configured to use it will glue itself to a single Deco node.

The problem is, that destroys the concept of a mesh. As well, when that Deco node goes down, devices connected to its Node SSID will lose Internet connection. Well, if you want device to connect to the specific deco, that's the price to pay.

I am not with TP-Link, but looking at this my guess would be, we won't see that implemented any time soon. I doubt any other mesh offers that, too - prove me wrong. 

Special case: Laptop stays connected to the main Deco rather than the Deco right next to the device.

If this is Windows laptop or tablet, you might be able to tweak WiFi driver settings. Google this: "Wi-Fi Roaming Aggressiveness Setting" 

One more workaround for Windows device. I have older Surface Pro 4 with WiFi adapter that does not offer WiFi roaming aggressiveness configuration. My Surface Pro 4 would lock itself to the closest node, but when moved around will only reconnect to a different node when signal goes really low. I mitigated that by enabling, under Wireless Properties, the setting “Look for other wireless networks while connected to this network” and by removing all known networks Surface Pro rarely connects to (from hotels and airports I used to visit, for example). 

It seems windows tablet started to reconnect to closest Deco node more aggressively after that.

Finally, on your Windows device you might find the option “Allow the computer to turn off this device to save power” under “Power Management” tab of network adapter. If you enable it, device should turn off adapter when it goes to sleep. When you wake device up, it will turn adapter on and reconnect to the network, ideally to the nearest node with the strongest signal.

Be warned - that might create its own issues with WiFi connectivity, but worth the try.