Everything I read says we need it.
What have you been reading?
You buy devices, and sell kits. Are the devices you buy in bulk form, such that you are adding the primary packaging and the only label? Or are they individually packaged, and you leave that primary packaging intact and place the packaged product into your kit overpack, which then gets an overlabel describing the kit's contents?
In the former case, you're probably a repackager/relabeler. In the latter case, you're only a kit-packer.
In either case, I think it's unlikely that it could be concluded that you have design responsibility.
The only circumstance where that
might apply is when a kit packer buys non-medical-device items from a general manufacturer, and--in the process of creating kits with them--re-purposes them for a clear medical device purpose. In that case, the kit packer is the most likely party to end up with medical device Manufacturer responsibility, and sometimes that can entail design responsibility so as to encompass the process by which a determination has been made that the product is suitable for the medical-device intended use.