I've worked at big successful F500 boring companies with polyrepo setup and it's boring as well. For this company, it was Jenkins checked out the repo, ran the Jenkins file, artifact was created and stuck into JFrog Artifactory. We would update Puppet file in our repo and during approved deploy window in ServiceNow, Puppet would do the deploy. Because of this, Repos had certain fixed structure which was annoying at times.
Pain Points that were not solved is 4 different teams involved in touching everything (Jenkins, Puppet, InfoSec and dev team) and break downs that would happen.
The short answer, start with a package management system like conan or npm (we rolled our own - releasing 1.0 the same month I first heard of conan which was then around version 0.6 - don't follow our example). Then you just need processes to ensure that everyone constantly has the latest version of all the repos they depend on - which ends up being a full time job for someone to manage.
Don't write your own package manager - if you use a common one that means your IDE will know how to work with it - our custom package manager has some nice features but we have to maintain our own IDE plugin so it can figure out the builds.
One full time job equivalent can buy a lot of tooling. Tooling that not only replaces this role but also shifts the feedback a lot closer to dev introducing the breaking change.
Every large project has this position. Smaller projects it isn't a full time job and so they distribute it amoung the team members and don't track the cost. Larger projects it is too large for a full time person and so they are forced to distribute the costs of this and just cannot track the costs. We happen to be in the sweet spot where a full time person can do the job and so we can track that cost. However make no mistake everything this person is doing is done on every project.
I agree with tooling being important. the person we have doing this job is a great engineer who automates everything he can, but there is still a lot of work that needs to be done. Some of it cannot be automated. (many of the problems are people problems)