So the quirk itself should be getting handled correctly, that’s part of going into the manage zigbee device, etc and configuring parameters there. I believe the code in question will be related to the verification within HA Core, and likely because the check there is just done against the cluster ID, which is the same across the 2-1 and Fan switches.
Re the device being considered a dimmer, this isn’t a ZHA issue per se, but it’s matching how the firmware is presenting the device. I’m going off memory here and could be misremembering, but I don’t believe Zigbee has a ‘fan’ device type. The only devices that support the ‘fan’ cluster are specifically HVAC devices, which this is not. It is possible to change the device type in the quirk (likely to something that would come through as an on/off switch), but device types by spec are supposed to have certain in/out clusters depending on what it is, so this may not be preferable either.
I recognize there’s a gap here between how those standards are set up vs user expectations though, and I believe that’s a part of why ZHA allows you to change the device type via the yaml configuration as well.