Sure, that might be possible too. But a gateway with an Ethernet connection is certainly more robust. If needed, RPI0+EnOceanStick+Ethernetstick+Box+PSU, but discreet is something else.
Yes, LAN might be possible, but it doesn't necessarily have to be more robust. I would tend to just test it first with the repeater, that would by far be the solution with the least amount of work. If that's not enough, you can always send the thing back and try it with a Raspberry.
All other gateways that come to mind spontaneously usually only offer the complete package including their own logic modules/app etc.