Is it a good thing that supermarkets have their own brands, typically cloning other packaging/branding and being at a price advantage due to not paying supermarket fees? Is this something we should try to protect?

All of these "What about x" points just make me think that we need to go further and stop those as well rather than using them as a justification to not bother.

I generally agree. But the "status quo" is to allow exclusivity deals all over by default, and it's worth recognizing that when trying to craft messages for lawmakers.