I've seen it NOT be the Wi-Fi way more times... My very first thing to look at is the current client connection. Option-Click on the Wi-Fi symbol on the top of your macOS screen to see all this available information. (or I like to use Adrian Granados Wi-Fi Signal for even quicker access.
First look to the MCS - if it is <5 than I continue looking for potential RF issues that may have caused that low rate. If it is >5 the RF isn't too much of a problem. If MCS >7 I really don't worry about the Wi-Fi. (MCS is a self-reporting for the transmitter...)
I check the Tx/Rx speeds reported by the Wi-Fi NIC... if these are above any Internet Throughput Testing results... again, I know there isn't a Wi-Fi issue.
If... on the other hand, the max Tx/Rx speed is the same as the Internet Throughput test... Now I know the Wi-Fi IS the limiting factor. Time to start drilling into what Wi-Fi issues are causing the slow down.
Could be client drivers, could be infrastructure... many times it is overly congested RF spectrum (check AP's reported Channel Utilization numbers and trends). Many times it is TOO MANY Access Points on the same channel, and they are all sharing the bandwidth.
All of this, and I don't even need to open a CLI window!!!
But if you are Windows guy... then follow the instructions in Dipal Thakkar listed in his blog post. (you might have to reverse engineer the data rates to find out your MCS rates though...)