Mostly agree. If you don't have capable designers and marketers on your team, you are severely handicapping yourself.

Also, while I might take money from an investor who doesn't have experience in these things, I wouldn't take money from one who doesn't have experience, yet insists on being involved in design and marketing decisions. It's amazing how many people feel the need to put their design/marketing stamp on a project, despite their complete ineptitude in those areas. I've seen it kill more than a few good ideas.