(GitLab employee but familiar with this because I use it personally as well)
You can always connect your own runners to GitLab, whether SaaS or self-hosted, and whether free/CE or premium/ultimate/EE. GitLab SaaS also comes with free use of the central runners up to a quota. I'm not sure about the history here but as far as I know this has always been the case.
Circa 2013? I remember vividly implementing gitlab at a certain cable company I worked at because they were too cheap for GitHub. I remember sometime in 2012 some merging of worlds of GitLab CI and GitLab.com, it was around that timeframe until 2015 or so when the unofficial runner because official and CI and Repos were merged? You work there, ask the oldest grey beard if this was the case. I could very well be mistaken and have false memory.
you might be right, especially in that time period new features were often EE only initially and then merged into CE. When CICD was first created it was its own software project basically, but it may have required APIs that weren't merged into CE yet. To be totally honest I forgot that CICD was around that early on.
You can always connect your own runners to GitLab, whether SaaS or self-hosted, and whether free/CE or premium/ultimate/EE. GitLab SaaS also comes with free use of the central runners up to a quota. I'm not sure about the history here but as far as I know this has always been the case.