OP has already confirmed they are getting full WiFi speeds on “some” devices.
Which proves nothing other than some of the time they get their full line speed.
So there’s undoubtedly zero issues with any of the stats or connection quality.
That might be the case, but your logic in asserting that as "undoubted" is fatally flawed: It is impossible to accurately conclude that the cable connection is fine by cherry picking a handful of wireless speed tests that show full speed being achieved. The very nature of DOCSIS makes it prone to intermittent speeds when faults occur. And since the hub stats are freely available with a few mouse clicks, it makes sense to check those early on.
It also makes sense to check the hubs stats in every case of poor wifi since the most frequent fix for poor wifi involves recommendations of buying equipment. Before spending money on new wireless kit, the OP might reasonably expect that the people proffering advice have the common sense to check that there isn't a cable problem.
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