Your SEO guy is right on some point but he doesn't know what he is talking about in another.
It is mentioned in more than one resource that the flow of the page is plus but it is not meant for search engine but rather the human. The picture you are referring to is true as human eyes go left to right then diagonal but that doesn't affect the Search Engine. Take WordPress for example you will notice that 90% off the templates have the navigation in the right column. Does this mean WP got it wrong!!!!.
As far as SEO you should always focus on product and category pages. Don't put all the effort in the home page. Would you rather have the SE send the customer to product page or Home page? I was a victim of this approach since my home page was stuffed with keywords. After 3 months of watching customer behaviors I realized that I am getting too much traffic for the home page with people searching for keywords not relevant to my website. So focus on product pages and categories less clicks and more conversion.
Always add content for customer and not SE. If you sell your page to the customer rest assure Google and other SE would move you up the SERP. Man Google is getting so smart, no place for games.
Finally read the article in the link above. Melanie has really done a good job in that post. If your looking for SEO "Expert" you should give her a shot :wink: