I haven't used Slackware, but all of the points you mentioned are valid for Arch Linux as well.
Frugalware may do a better job for that (if you love Arch Linux, but don't want to use it on production you should give it a look!), but still isn't Slackware.
Personally if someone would have put LFS in front of me when I was just starting out with Linux, I would have freaked out. It's just too complex (although not complicated) to get up and running. But it's a good learning experience once you're comfortable with the basics.
As for Arch, it was one of my stops when I migrated away from Slackware, and while it's very similar in some aspects, I feel it has an added layer of fat that's missing from plain Slack and its one man vision of what a distro should be.
YMMV and all that, but IMHO Slackware is a Goldilocks distro. It maximizes learning without the pain of being overly onerous.