Do I have to leave WordPress or my current CMS?

Not automatically. Some sites are better connected than replaced.

What matters is whether the site can be worked on reliably and whether it can be instrumented. A well-maintained CMS site with server access is a different situation from one carrying years of plugin debt that nobody can safely change.

We will tell you which one you have. If a rebuild is genuinely cheaper than repair, we will say so, and if it is not, we will say that too.