First, anytime you stick a device in the middle you will lose some speed. Also, you didn't reveal if the router firmware was current or settings in the router.
https://www.cnet.com/products/netgear-n600-wireless-dual-band-router-wndr3400-series/review/ doesn't tell me this is a bad router but it is middle tier.
Retest but only with current router firmware and all stock settings.
I just got off the phone with Comcast because my download speed was about 45Mbps with ethernet cable plugged into router. I plugged the Ethernet cable directly into the modem and my speed now exceeded the 75Mbps that I am paying for. I have a Netgear N600 WNDR3400 router. I have tweaked settings on the router many different ways, but still the same results. I even researched the difference between a cat5e and cat6 Ethernet cable. Does anybody have any ideas on how I can get true download speed or close to it when the Ethernet cable is connected to the router instead of directly into the modem. I just bought a new Netgear DOCSIS 3.0 modem. They said my Motorola DOCSIS 3.0 was at EOL, but that's crap. Thanks. Jay @ HP software engineer.

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