"So ... you are saying when you went Asus to Asus, eyuch and when you went Netgear to Netgear, eyuch but when you went Netgear to Asus all is well?"
Well all is faster. AIMESH mode was the slowest throughput of them all. But it was plenty stable once configured. I think technically it would be Asus to Netgear. The Asus is the slave.
If I reasonably could I'd run a cable. Its possible but I'd need to pay someone as my vaulted ceilings make me doing so unwise. At this point I might get a little more performance being hard wired but probably not much.
Even if I was doing AIMESH or some kind of wireless repeater mode, not media bridge mode, I'd still look at external antennas. Gives you so many more options for placement and wifi signal strength testing. I was very surprised to see large swings by even small location changes. The typical W pattern also was not the best performer. Two straight up and one straight down works best for my application.
If it is the case you're looking just to extend wireless access I was very happy with the performance of the higher end Netgear wifi extender or the TPLink 1733 capable one. I did not test any of the Asus ones, not sure they have one, or the Bluecube thing as it would be used that way in pairs, etc. IF in your setting and logistics its possible to run cable at least to the wifi extender and set it up in AP mode, you'd extend your wireless network and have only one router to contend with. The higher end ones usually have at least one ethernet port to do just that. Netgear's higher end as four LAN ports.
Also you could consider an 86U, I really like it for price performance, and set it up in AP mode. Again IF you could run cable part way and not all the way to the zone that needs better coverage. My opinion is wired to a router configured in AP mode is the best way to go. You extend your wifi coverage and have a network switch to boot.
I looked at power plug adapters. As far as I can tell they do not perform where I'm at now. But if you're not needing blazing fast speeds they do work and you can configure zones, etc., with them. I'd not but they do have a place or purpose.
Interesting as well is if I set the Netgear to HT160, I have no HT160 devices and the Asus 86u is not, I get between 2-4db boost in wifi signal. I go from -46/-47 to -42/-43. MU-MIMO and beam forming decrease signal strength. HT160 on in the Netgear R7800.