Where plugins help
They are useful for titles, descriptions, open graph fields, robots controls, and some schema defaults.
Where they stop
They cannot clean a slow template, weak internal links, accidental duplicates, broken redirects, poor product data, or JavaScript output that search engines cannot read well.
What matters
Crawl paths, canonical URLs, robots behavior, sitemap output, product schema, page speed, content hierarchy, and redirect behavior need to be checked together.