Not my experience. The CI systems I dealt with most recently, for example, were very much compute-bound. Way too weak VMs for the runnres, and way too few of them. With CI builds taking each of upward 2h, and capacity to run maybe 10 of them in parallel, this pretty much destroys any ability to work with small commits - you have to squash them before submitting for review anyway, otherwise you destroy anyone else's ability to get their changeset through CI for the rest of the day.
This is entirely solvable by getting more resources. At least 2x more runners, each at least 2x as beefy. You could go 10x and I doubt it would be anywhere as expensive as the amount of money company wastes on devs waiting for CI. Alas, good luck convincing people managing the infra of this.
There was caching of third-party dependencies, but at least 2/3 of the time was spent on various tests, which for domain-specific reasons weren't trivial. Sure, everything there could be optimized further, but this is a textbook case of a problem which can be solved by adding more compute for a fraction of the cost of dev-hours spent trying to optimize compilation and test times.
This is entirely solvable by getting more resources. At least 2x more runners, each at least 2x as beefy. You could go 10x and I doubt it would be anywhere as expensive as the amount of money company wastes on devs waiting for CI. Alas, good luck convincing people managing the infra of this.