The Linux kernel uses the CPU default scheduler, CFS,
Linux 6.6 (which recently landed on Debian) changed the scheduled to EEVDF, which is pretty widely criticized for poor tuning. 100% busy which means the scheduler is doing good job. If the CPU was idle and compilation was slow, than we would look into task scheduling and scheduling of blocking operations.
I'm not sure if you understand what swap actually is, because even machines with 1Tb of RAM have swap partitions, just in case read this post from a developer working on swap module in Linux https://chrisdown.name/2018/01/02/in-defence-of-swap.html