Branding can be important to the bottom line of the private sector, plain and simple. It's why you make something look attractive, so that people know, “I want the product in the red package because that's the one my dad uses”, whatever that product may be.
Nothing about plain packaging prohibits the provision of clear information about potency, outcomes, and potential side effects of use of the product. We need to not glamorize cannabis consumption the way we previously glamorized tobacco and continue to glamorize alcohol. This is not an industry that needs help selling its product, so it's a complete red herring that the poor industry isn't going to be viable if they don't have these rights given to them. They want to be able to market as strongly as any other industry wants to market itself, but there is no need for it. We have a proven marketplace in Canada already.
As far as competitiveness with the illegal market, which won't disappear overnight, the studies in Washington state and in Colorado have shown that when they have the option, people prefer to go to the legal option. Even if it's not exactly the same product they're used to, and even if it's slightly more expensive, they would rather not risk a criminal fine by purchasing an illegal product.
Once again, legalizing and regulating is helping the legitimate industry, and we will eventually see a reduction in the illegal market.