WordPress is not slow. Careless WordPress builds are slow. Here is the difference in practice.
WordPress runs a large share of the web, including plenty of very fast sites. When a WordPress site is slow and fragile, the cause is nearly always the same: a bought theme, a page builder and twenty-something plugins each loading their own scripts and styles on every page.
Model the content properly
Services, projects, listings and team members should be real content types with defined fields. Editors then fill in meaningful boxes instead of rebuilding layouts by hand, and the design cannot be accidentally broken.
Be strict about plugins
Every plugin is a dependency, a security surface and usually some extra front-end weight. A small number of well-chosen, well-maintained plugins beats a long list that overlaps.
Then the usual performance work
Optimised images in modern formats, sensible font loading, caching at the server, minimal JavaScript and no scripts loaded on pages that do not need them. Done together, these turn a typical WordPress build into a genuinely fast site.