You are asking too much of a piece of hardware.
To be fair, it's not asking much to want motorways excluded without all highways excluded. It's only expecting Garmin to understand cycling that is too much, sadly.
Yes, that's basicslly correct.
But this is an issue with the maps, not the hardware.
The City Navigator maps are basically road maps aimed at motorists.
Where the roads co-incide with the cycle routes, they work well.
Where the cycle routes deviate from the car-roads, then generally fail.
Examples:
Forth Road Bridge.
The maps don't know about the cycle-way, and route you onto the main road, the A90.
The Barmouth Bridge ( onthe BCM600 ).
The maps don't know there's a cyclway, and try to route you via a massive diversion.
You need to pre-plan the route on the PC, and inspect where the route is going to take you. You need to be prepared to deviate from the route at certain points. Having a track displayed underneath the route will help you see where these deviations are.