XB10 and X-class service, 500 Mbps down / 35 Mbps up

Hello, recently I have changed Internet plan to 500/500, as the Xfinity agent suggested that X-class is available in my service area. As a part of this upgrade, I got a brand-new XB10 gateway, apparently required for 500 Mbps and faster uploads. 

When running SpeedTest from Comcast website or locally, my actual uplink / downlink will max out at 600 Mbps down / 40 Mbps up. I have run the test connected to the gateway over Ethernet or Wifi, no difference, so this is not a bottleneck between my desktop and the XB-10 gateway. This is clearly not symmetric throughput promised by DOCSIS 4.0 spec and supposedly by the XB10 hardware.

When looking at my current plan on the Xfinity website, it says "500/500", but then spells out "500 Mbps download and 35 Mbps upload speed". I had two Xfinity agents look into this, they insist that yes I am in the X-class service area, and no they don't have ANY plans with uploads faster than 35Mbps (faster than 35Mbps will damage your device... huh, what device???) 

Before I give up, return the XB10 gateway to the store, and accept the fact that I was tricked into getting the Internet plan "upgrade", let me ask: is there a higher tier Xfinity technical support, someone who can have a look and confirm that this is not some XB10 provisioning error, and not some on-premise issue, like some filter on the cable-to-home that they forgot to upgrade?

I wish there was a Google or Sonic fiber available in my neighborhood so I could switch over. Unfortunately for wired network we only have Comcast cable or AT&T DSL. Maybe I shall seriously explore wireless options like Starlink or Verizon 5G.

Cheers,

One utterly confused Comcast customer