WP is terrible for SEO, and no plugin can change this.
Someone PMed asked me to explain my statement. This is the reply I sent him, with the example sites removed.
WordPress is a content management system. it is designed to deliver the written word in a particular fashion, and make it extremely easy to find this information.
Since you cannot really effect the code in WordPress without hacking the core, many of the seo functions have to be filled in by a plugin that inserts them into the correct tags.
While this is fine for the title and description, it does nothing for heading tags.
In SEO, the content in the heading tag is weighted. Depending on the tag, the contents are given more weight than other words on the page.
The h1 tag is critical and you are allowed only one. The contents of this tag are the second most valuable for SEO on the page, it is supposed to be the main concept of the page. The h2-h6 tags are used for more information to support the tags above it.
In other words if your title is how to fish, your h1 (You are allowed 1 h1 tag, period. There can be only one) tag should re-enforce that. so
Title How to fish
H1 Fishing basics for beginners.
The h2 tags are supposed to support the previous h1 tag, so:
Title How to fish
<H1> Fishing basics for beginners.
<H2> Rod and reel
<h2> Cane Pole
<h2> Trout lines
In the above example, you will see that the title sets the subject of the page., the h1 reinforces the subject matter, and the H2's give more information about the contents of the H1.
If an h3 is used, it should support the h2 it is under, so:
Title How to fish
<H1> Fishing basics for beginners.
<H2> Rod and reel
<h3> Fly Fishing
<h3> Open faced reels
<h3> Closed faced reels
<h2> Cane Pole
<h2> Trout lines
By giving more emphasis for the words in these tags, you can tell the search engines exactly what the content is about. You are saying these words are important to the page.
Here are some Typical h tag structures from wp sites I have looked at in the last week.
XXXXXXX LINK REMOVED XXXXX
Not that there are 3 h1 tags, one for the page title, one for the article content title, and in this case, a blank one that affects how large the logo is. In addition to that, the H2 tag is a duplicate of the H1 tag for the most part.
This is because this theme uses the h tags to control font size, so any sub headings on the page will all be h2.
XXXXXXX LINK REMOVED XXXXX
You should be able to see the problem this introduces by now. No h1 tag in use, so the second most valuable piece of SEO information (aside from the title) is missing from the site. This is telling the search engines that "leave a reply cancel reply" and "men and women" is very important to this page, but this content is not supported by any other information on the page.
WordPress is designed to allow anyone to build a website that will display correctly, but it comes with default behavior behind the scenes that you never hear about.
If you have a page about a horse the vet treated that had stomach bloat, and you put it on your site about horses under the category "Equine health problems", and "Feeding horses the right way", WordPress will create one page and have two URL's pointing to it. (site.com/equine health problems/bloat, and site.com/feeding horses the right way/bloat). This will cause the search engines to think there are 2 pages on the site with the same content, because there are two URLs pointing to this page, which incurs a duplicate content penalty.
The content of a page includes all the content on the page. If you are using WordPress, there are areas of the theme called global areas. These areas display on every page or post, and if you don't put something there, the theme will just throw a default content there.
Think about what this means. You have a superb article, 500 words with razor sharp focus on your keyword, and you add it to a WordPress page.
When it displays, the page content will also include all words used in the navigation, sidebars and footers. You have just destroyed the keyword density and focus of the article, unless you adjust the article to restore the focus with this additional content taken into consideration.
You get seo points any time text composes 50 % of the full content on the page, in other words if your page is half code or smaller, you get points, but if it is over 50% code, you do not get these points.
In both of these examples above, because WP is a code hog, the ratio of text to code is 17%. This means that if your page has 100 words on it, 17 will be content,and the rest will be the code to display the content.
This is a typical percentage of code to text for WP.
There is more, but I hope I have answered your question.
Like anything, WP is most excellent for what it is designed to do, which is to deliver the written word Once you start hanging plugins on it, you are not using it for what it is designed for, and like anything, the efficiency goes to hell.
I can haul logs in a school bus, or take children to school in a log hauler. But no matter what I do to those vehicles, they will never be optimized for the task I am using them for.
WordPress is not designed for SEO, it was stuck on as an afterthought.