
eero
Pro 6 Series
Easy, reliable, smart home ready; but paid features.

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Short answer just keep the 3 decos return the archer. The other option is to return the decos, and buy other easy mesh nodes to expand the archer easy mesh. It's really confusing the 3 different incomparable TP-Link lines As I understand it. Deco: simple, plug and play Easymesh: more features and control inter-brand compatibility. Omanda: more expensive, prosumer, allows and requires more configuration.
You need an wired backhaul wifi mesh system like omada or unifi. https://youtu.be/n34oT8mZetE?si=RTywTOV0BXaqUrxh
While running cable/fiber is the "best" option, I do recognize it's not always an option. I have a different orientation, but similar needs and I'm using TP Link Omada. It's been great and going strong for about 3 years now. Setup was not that difficult, and it has more advanced features if you want them. You will need a router, a switch, at least one access point for each building, and a bridge kit. There are newer options now, but when I put my system together I went; - ER605 V2 router - OC200 controller. Not absolutely necessary, but makes it way easier as it basically plug-n-play instead of using the cloud version or installing it on my own machine. It's a little slow, but it gets the job done. - EAP610 access point in the house. - EAP225 outdoor access points, x2. These can be used in a wireless backhaul quite effectively. I did this for a while until I was able to trench in my fiber and backup Cat6A lines to my shop. - TL-SG108PE switch. It's an 8 port (4 POE, 4 Regular) switch that gets you up and running. - EAP215 wireless bridge kit, just added this as it can be used as a Ptp, PtMP, or AP and is managed through the Omada Controller. I just went to Amazon and this hardware listed above is currently $450. No if you add an AP(EAP610) each for buildings 2 and 3, and only one EAP225 for additional outdoor coverage you are at $642. Picking up some patch cables, Cat6A for the in house run to the bridge, maybe a mini-rack and shelves to keep it nice and tidy and you're right around $1000.
We went from a eero 6E to new TP-Link Omada stack. Eero worked surprisingly well for very basic, no config, home requirements. We need VLANs and VPN so made the switch and couldn’t be happier.
I have had both Unifi and Omada. You can't go wrong with either. I switched from Omada because Unifi had cheaper 2.5gb switches at the time. The Unifi controller is a little better than the Omada one.
If you're wiring, choose something better than consumer meshy stuff. I would second the UniFi recommendation, and TP-Link Omada is good also. Wire everything that *can* be wired and save the wifi for those things that can *only* use wifi. The UniFi Cloud Gateway Ultras as the router/controller and whatever switches you need, plus the APs of your choice U6+ or U7+ are good would be a great setup with fully unified management of the network and components.
In consumer world - Asus and TP-Link are the better choices. Eero is great hardware has a subscription model for some needed (IMO) features. I would avoid Netgear, D-Link and Linksys - they are not what they once were and have subscription models, sometimes poor support, and varying reliability and quality. You could also consider gl.Inet Flint devices if you're looking for an all-in-one router, they have gained a very good reputation. I agree that a better choice than any of the above would be Ubiquiti UniFi and TP-Link Omada is also decent - it's different than the consumer gear. Reliability is one of the major points of these prosumer setups. I've been running UniFi for 7 years, it's great.

eero
Pro 6 Series
Easy, reliable, smart home ready; but paid features.

TP-Link
Deco XE75 Pro
Great coverage, easy; but unreliable Ethernet, poor app.

eero
eero Max 7
Incredibly fast, reliable; but very expensive, limited control.

eero
eero Pro 7
Fast, reliable; but paid features, needs internet to function.

eero
eero 7
Easy, reliable coverage; but no 6GHz, paid features.