How are you testing failover?
Are you shutting the port channel and interfaces down completely?
When you do this, does the route change on the cisco side (i.e does it remove the first default route?)
The route wont drop from the table unless the physical interfaces are down or you are using some kind of tracking / IP SLA.
I dont understand your intended cabling changes, it looks like you are trying to take a cable from each port channel to each SRX?