Slow WordPress sites are usually slow for a handful of identifiable reasons: render-blocking bloat, unoptimised media, chatty plugins, bad caching. Performance work starts with measurement (field data where available, lab tests otherwise), fixes the causes, and verifies with before/after numbers you can check yourself.
Technical SEO is treated the same way: correct canonical logic, clean sitemaps, valid structured data, sane redirects, and an internal linking structure crawlers and humans both understand. No ranking guarantees are sold — those are not honest — but the technical floor is made solid.