@Zorro16 

My understanding is, this is what you want:

You can have that with Deco mesh running in Access Point mode. By default Deco will run in Router mode, but after you added first unit and it became Main Deco, you can switch Deco mesh to run in AP mode: Switching a Deco to Access Point (AP) Mode

Archer AX73 will not share WiFi with Deco mesh, while these are products from the same brand they are not WiFi mesh compatible. Treat Deco X50s just like you treated Apple Airports before: a system to provide WiFi coverage for your house independent of Archer AX73.

  @Зорро16 

Not quite on topic, but I’ll answer anyway.

in your case, I would consider the Omada corporate solution as wifi access points

I understand that you have an organization or something similar, deco is positioned as a home solution or a solution for a small office

in deco there is no control of wifi channels, and in access point mode there are generally no functions for managing a wireless network, they are quite meager.

if you have a server, you can deploy the omada software controller, or buy an inexpensive tp link OC 200 as a controller

I can recommend the access point EAP 660 HD

  @Zorro16 

You may mix the decos with the router, but by doing so, you will have to set the Deco into AP mode, and you will need to forego on QOS,Parental Controls, NAT, or some other features that MAY or MAY NOT be listed out in this forums.

Read here for the differences for Router mode and AP mode on Deco
https://www.tp-link.com/my/support/faq/2399/

So, if you want FULL FEATURES of Deco, best to use only DECOS in the network, if not, you won't be facing any issues by linking one Deco to the AX73 router with LAN cable and the rest as wireless backhaul.

  @Alexandre. 

Thank you for this. Yes, that diagram sums up the set up I would like to replicate in our home. It's a large one-level home with brick walls and an internal courtyard. We effectively have the Archer AX73 in one corner of the building and the airports in the other 3 corners to give us coverage. Airports are all set on "Extend a Wireless Network" which sounds the same as Access Point mode on the Deco units. This works well except for the looming speed issue.

I guess the obvious question is "To replace that set up, why go for the more expensive Deco units when 3 good Range Extenders (eg TP-Link AX3000 Mesh WiFi 6 Extender) in Access Point mode would achieve the same result for less outlay?"

May I ask if you see any obvious Pros and Cons of that option (other than the obvious "future proofing" by investing in Deco units now and a newer Mesh-compatible Router down the track)?

Thank you inadvance for any further guidance you may have.

  @Godlike66 

Thank you for this. The set up is for a home... but a large, spread out, one-level home with internal brick walls. So the 3 Deco units or similar would be necessary.

I'm not tech savvy enough to consider Server options. It will have to be simple and idiot-proof or I will mess it up!

Thanks again for responding so quickly.

  @Omochao 

Thank you for your response and the article link. I'm not sure I'm tech savvy enough to utilise all the features that I would forego by using the Deco units in AP. Range extenders would do the same job for much less money.

I think my decision needs to be based on whether I future proof our set up by going with Deco units and a new Mesh compatible Router, or save the money by simply range extending with 1000 mbps units for now.

Thank you again for your advice.

  @Alexandre. 

Thank you yet again for your quick and easily-understood response.

From reading the articles you and other community members sent, it seems that the combination of our current Archer AX73 Router and 3 x RE705X Range Extenders will give us the coverage and speed we need at a pretty good price point. All are OneMesh compatible and the RE705X accepts wired ethernet. 

I really appreciate the time you've taken to assist me.