Your RSSI (raw signal level is an good -57 dB, where -40 I=s right next to your Router, and -75 is unusably low. so you are NOT too far away form your router.
Using two antennas and a modulation pattern with 64 patterns per signalling interval, you have attained a respectable 527 M bits/secs speed.
You have connected on the 5 GHz band, using an 80 MHz channel centered around channel 35, using 802.11ac rules.
This does not appear to be a Mac hardware issue, and not likely a Router issue.
But if you connection is slowing from time-to-time through the day, or getting even slower and disconnecting, that could be caused by other nearby Routers using the same channel. When they start a big data transfer, it could knock you off the air.
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The usual way we do this with ONE Router and No boosters is the set the Router to "automatic" channel selection. Then when the Router powers up, it listens momentarily to what is already on the air, and adjusts to the least-busy channel.
it is not an accident that every debugging procedure starts with "cycle the power to your Router."
The next level we can use is to use the SCAN tool in Wireless Diagnostics to look around at what is visible over the air around the Mac. This has the advantage of showing what is seen at the Mac, which may be slightly different than what is seen at the Router(s).
this is what it looks like:
(drag and drop on Preview to see larger, or make your own)
Click on the channel column to sort by channel. This tells you the nominal channel in use, but every channel also spreads up and down the channel numbers, depending in its channel width. For example, channel 36 at 80 MHz wide spreads to engulf everything up to channel 48. You may need to look up the spectrum spread with some tables, available online. Or post back here and readers can look those up for you.
