On my Gentoo, I did parallel boot for a while in OpenRC. I didn’t like it. It was disorderly.
I didn’t like it, even though I had slow hard disks rather than fast SSDs.
Gentoo can use systemd, but I never used it. We had to use PARTS of systemd, because of the authoritarianism. The shoving of systemd down our throats to keep things like udev and whatnot working. But OpenRC remained the default init system, thank goodness.