The rt1800 can be flashed with open wrt giveing you alot of control

https://openwrt.org/toh/hwdata/belkin/belkin_rt1800_v1

However it seems your spectrum device is 4x4 mimo vs the belken 2x2.

https://fccid.io/VW3FAST5285/Test-Report/Test-Report-5GB1-B4-4851412#google_vignette

So aside from the improved control it would be a multi client wifi performance downgrade.

The belken should beable to nat you connection. So the main difference is control or extra wifi bandwidth between multiple devices.

Yeah it's through coax and I have a separate modem from the router.