WiFi connectivity issue (5GHz, MacBook Pro)

You have a really strong, excellent signal strength at -53 dB. You must be right on top of your Router. (I use "better [closer to zero] than -50" as a talking number to describe what you should get right next to your Router.)

You appear (derived from a chart on Wikipedia) to be using three antennas, but only attaining MCS index 2 out of a possible 9 using that method and attaining a Transmit rate of 264 where 1170 is possible using that setup.

I immediately attribute the difference to your neighbors. If your Router is not already set to "Automatic" channels selection, it should be. Then when the Router powers up, it will select the channel with the best reception (least busy and best throughput). It is not an accident that every debugging procedure starts with" cycle the power to your Router."

You can look at what channels are in use by your neighbors using the tools in Wi-Fi diagnostics (also invokable from the Option-Wi-Fi menu). Choose Scan for a look at what channels are in use and how strong these signals are:

(drag and drop on Preview to see larger)

DON"T select Diagnostic Report, it is a waste of time. It should be named "Diagnostic DUMP" and his no summarized report at all.

Note that Scan shows only the nominal channel, not the "spread" up and down. To see the full spectrum in use an inexpensive third-party utility like Wi-Fi Explorer (available with 3 -day trial) can be very useful:

(drag and drop on Preview to see larger)

.

Have you recently cycled the power to your router to see if it still wants to stay with channel 36 since the last time it powered up?

Post the data from Option-Clicking on the Wi-Fi Icon, like this:

and also, how many Networks do you see?