I have two clients with 15” 2018 MBPs running macOS Catalina. Both laptops only get 125 Mbps down with wifi even though other MacBook Airs and non-2018 MBPs in the exact same location get about 400 Mbps down.
I tested the heck out of it and deleted and re-added the wifi settibgs, etc, etc. etc.
One client has tip top of the line wifi — Ruckus AC with a Zone Controller (each AP is about $1,200 and hard wired and a $800 Zone Controller manages them). I examined the connections in depth on both the zone controller and by option-clicking the Macs’ wifi icon (confirmed 5GHz and connection to closest AP).
After seeing the tests with other Mac laptops getting much faster download speeds at the same location, one client replaced the 2018 MBP with the latest available MBP around Jan 2020. Its wifi gets the max possible (about 400 Mbps).
The other client has a new Amplifi HD Mesh system and even when right next to cube router, his 15” 2018 MBP only gets about 125 Mbps. He uses an Ethernet adapter to get 900 Mbps up/down.
There seems to be something wrong with wifi in some or all 15” MBP 2018 models. Older and new models in the exact same spot running the exact same macOS version get about 400 Mbps while 2018 15” MBP get about 125 Mbps.
This might not be apparent to most users of 15” 2018 MBP models who have internet service slower than 125 Mbps or who don’t notice performance problems with ~125 Mbps down, since that’s good enough for most services. But with more and more video conferencing and increasingly common internet connections faster than 125 Mbps, some users like mine have noticed.
. Often times this problem is compounded with multiple wireless devices chatting amongst themselves, so even half the bandwidth available as throughput is a win. It may often be less. This can be somewhat mitigated by selective channel and frequency allocation of devices, and this practice is likely to provide better results than throwing money at a wifi 6 router in many circumstances I would think.
