Recommendation for a Linksys MR5500 replacement with good coverage

Hi all,

I was very happy with the Linksys MR5500. I removed two repeaters because the coverage is very good and I no longer need them. I used it as an AP with the original firmware behind the ISP router.

Now I am planning VLANs, so I bought a Flint2. However, I feel like I have gone backwards because the signal coverage is not good. Before, I had a Belkin RT3200, and before that, a Netgear R6800, which had similar coverage when I needed two repeaters.

Here are some numbers for the MR5500 vs GL-MT6000 in one of the corners where I use Wi-Fi:

Router 2.4 GHz 5 GHz
MR5500 -66 dBm on channel 9 -75 dBm on channel 149.
MR5500 attempt 2 -65 dBm on channel 9 -55 dBm on channel 36.
GL-MT6000 Flint 2 -79 dBm on channel 13 -84 dBm on channel 40.
SPNMX56 -54 dBm on channel 1 -65 dBm on channel 36.
GL-BE9300 -72 dBm on channel 6 -70 dBm on channel 36.
GL-BE9300 6 GHz -55 dBm on channel 5 (6.GHz)

I tested one device after another with WifiAnalyzer on an Android phone. It's not a busy area. There are -82 dBm and -93 dBm neighbour routers on the 2.4 GHz band 1 and 6 channels.

My goal is to avoid repeaters and manage VLANs in tandem with a Level 3 switch (eg. Cisco 3560CX). I am not keen on the idea of double NAT, but we will see.

Questions:

1. Is there a good coverage alternative to replace the MR5500?
2. If I install OpenWRT on the MR5500, will I lose signal coverage?

Context:

The MR5500 was shipped from the US market. There are possibly different regulations, but there is no option on the original firmware. I am aware of the 5 GHz channels with a possible higher power limit of 100+ channels. However, the original issue was that some IoT devices lost their connection after the change to Flint2. My Android phone also switched to 2.4 GHz in some places, whereas it normally operates at 5 GHz. Both with original firmware. I.m in EU. My network is ~10 PCs and Androids, 20+ IoT.

I tested two more routers and retested the MR5500. I was impressed with the results on the 6 GHz band! There are two concrete walls and a distance of over 10 metres. I have just installed OpenWRT v.25.12.2 on the SPNMX56 (MX5600) and the original firmware on the Flint 3. I have added the results to the first post.

I'm shocked that even the top GL.Inet Flint routers don't have such good coverage on 2.4 GHz. I was also impressed by the Linksys's Beamforming technology. The internal antennas on the SPNMX56 (MX5600) are far better than those on the top Flint routers.