'Broadband connection through usb tethering vs direct laptop wifi

I have a broadband connection. When I connect my phone to it and then do USB tethering to my laptop with my phone, I'm getting >20mbps speed on speed test. Now if I directly connect to that broadband connection using my laptop wifi, then it is giving speed like =~ 4mbps. Why this is happening and what's the fix for this weird issue?



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