Apt has been painfully slow since I started using Debian last millennium, but I suspect it's not because it uses a lot of CPU, or it would be snappy by now.
In normal operation, apt has to be able to upgrade the kernel, the bootloader, and libc, so it can't usefully be sandboxed except for testing or chroots.
Apt has been painfully slow since I started using Debian last millennium, but I suspect it's not because it uses a lot of CPU, or it would be snappy by now.