You are using the very crowded and interference-prone 2.4GHz band. Rather than the standard channels, 1, 6, and 11, your Router is using channel 8. I do not know if it chose that channel "automatically" or if you had to intervene to set it to channel 8 manually. (In some very busy cases, using an in-between channel can improve a desperate situation.)
your RSSI of -51 less typical noise at about -85 gives a signal strength of about -34, very good signal strength. Using 802.11n, you have the capability for a base speed of about 54M Bits/sec, and the ability on a not-too-busy channel with an advanced Router to send two or three streams to double or triple the data rate. Your Transmit Rate of 54 shows that your Router is not attempting to double or triple, either because it can't get the additional data through, out because that Router is too old to have that capability (which requires multiple antennas).
10 competing networks are extremely likely to all be using the 2.4GHz band as well, so you are trying to shout over all of them. There are only three standard channels in this band, and moving to an in-between band means your signal collides with other on both sides, since each 802.11 channel sprawls up and down two additional channels. (e.g., channel 6 uses 4, 5 ,6,7, and 8)
You could benefit from a replacement new or added new Router, that has 5 GHz band capability, which would open up all the channels higher up, which are wider, less busy, and less subject to interference, but slightly harder to pick up. You already have very good signal strength, so moving to a higher band would not be a problem for you.
Your problems are caused by existing conditions and the Router you are using, not by settings or deficits in MacOS.