Inspiron 15 3521 Ethernet Top Speed 50Mbps?

Hello.  This is not a question but rather a request to confirm what I've tested and discovered.  My son's Inspiron 15 (3521) when connected via CAT5 Ethernet does not seem capable of exceeding 50Mbps.  This is similar to the WiFi speeds the same machine gets.

Background: Our house subscribes to 300Mbps internet. We have 4 computers in our house. Three computers show a download speed via speedtest.net of just about 300Mbps -- 2 Desktops and a Surface 3 (via WiFi 5G.)

The Inspiron 15 3521 however, has never tested higher than 48Mbps. It's running Windows 10 with the latest drivers.  I even plugged an Ethernet cable from one of the desktops' 300Mbps connections to the Inspiron and the Inspiron still registered in the 45-48Mbps range.

So here's my question/concern/request to confirm:

Is that all ya got?  Is the Inspiron 15 (3521) only capable of 50Mbps Ethernet and incapable of anything faster?  That's the only conclusion I can reach based on my testing.