Content is King
This is a true saying, and well worth remembering. After years of all manner of ways to try and trick Google into giving us better results that we would otherwise get, the Google search robots now focus on the text being delivered to the site visitor, far more that keywords, meta tags, and the other mechanisms.
Now no one understands your business like you do. No one can tell the story of your business more authentically than you can. So it would seem that that is the place to start. Having said that there are some pitfalls, so once you have it written, then it is time to talk to someone who understand the web, and the problems to do with readability scores, complex sentences and technical terms.
Working together in this is likely to give you the best result. When the web designer is the source of the content, it may be technically good, but it will lack the heart of authenticity that it needs to provide real content.
People do not visit websites for the flashy things, but rather to find content.