IF the RC passes the “events” to HA(in some way), instead of Device/Gateway, the RC won’t work if HA is down … thats the whole point, of having the “Gateway” ( controlling devices from APP in i.e.phone or HA)… AND you can flash/program the ikea (5 button RC’s) but still It’s “talking” Zigbee, so how would you ever get a Device (laptop, Pi, NAS , whatever HA “nest on”) that is not build for sending/receiving Zigbee to “respond” to a Zigbee-signal ? … and in regards to your last “commend” … i don’t know what you are “not happy about” , where / to what did you paired your RC’s to, a tradfri-outlet(plug), a Tradfri-Driver ? , Do you have a Tradfri-Controller(hub), and “paired/repaired” any Devices yet ?
PS: The “event” if passed from HA, goes through the “Gateway” to the Device, The events/state from a “Device” goes Through the Gateway to HA , but yes you could “flash/programme” your RC to use for other(or maybe ikea) Zigbee devices/gateway … but still the “state” does come from the Device you are controlling