Again and again I've heard people like you suggest that Slackware is a replacement for a modern mainstream distro like Debian. Others suggest Gentoo.
Well, the reality is that neither is sufficient.
Slackware is, to put it politely, very primitive. While simplicity is a good thing, Slackware takes it to the point where it becomes a liability.
When using Debian, it's possible to get a full-featured desktop or server set up with very little effort, and this can be done quickly. Thanks to sensible defaults and a practical installer, manual configuration is kept to a minimum.
Slackware, on the other hand, requires far too much manual intervention just to get a minimally usable system set up
Please define primitive, very little effort and manual intervention.
I can have a fully functioning Slackware system up and running in 30 min, including formatting the HDD with very little manual intervention.
Slackware 14.2 is about to be released. It boots either BIOS or EFI and runs Linux 4.4.11 and a number of Desktop Environments, all without systemd.
There is now a set of 'slackware live' ISO images where I can run with persistence and optionally encrypted from a USB Drive:
a complete 64bit Slackware-current Live Edition (in a 2.6 GB ISO);
a slimmed-down XFCE ISO (700 MB) with XDM as the graphical login manager. It fits on a CDROM medium or a 1 GB USB stick;
an ISO image (3.1 GB) of Slackware64-current containing Plasma 5 instead of KDE 4, with an addition of several other packages from the alienBOB repositories: vlc, libreoffice, calibre, qbittorrent, ffmpeg, chromium, openjdk, veracrypt.
a Mate variant (1.7 GB) where KDE 4 has been replaced by Mate (a Gnome 2 fork);
a Cinnamon flavour (a fork of the Gnome 3 Shell replacing Slackware's KDE 4).
a Custom variant which you can give your own name, its own package list and custom post-install configuration.
When I like what I see, there is an option to install liveslak to the HDD.
As I said Slackware 14.2 is about to be released. This version has succeeded in leaving systemd out while still being able to run the most recent releases of upstream Apps.
Have you actually looked at Slackware ?
There's a lot to like.