It's not the oldest. SLS predates slackware (as do a few others iirc)
https://en.wikipedia.org/wiki/Softlanding_Linux_System
Slack was awesome back in the day, but the the philosophy as being "as unix like as possible" prevented it evolving and adding nice things like package managers. Using slackware is a good exercise, but I'd never use it for an application I care about.
If you only need a couple of applications, it's great. We use it for 200+ POS terminals for our ERP/CRM software. It's obscure enough that the end users have no clue how to mess anything up (aside for occasional icon deletion in KDE, but even that needs the "unlock" step).
> the philosophy as being "as unix like as possible" prevented it evolving and adding nice things like package managers
Others have pointed out that the existence of Slackware package management gives the lie to that assertion. It remains to point out that Unices had package managers, so being "Unix like" does not involve eschewing package management at all. XENIX had a package management system, for example. It originated in AT&T System V Release 4, was also present in Solaris, and has been picked up by the Heirloom Project.
This is simply false. Slackware has a package manager. It just does not resolve dependencies. It has also evolved. The Slackware developers have worked on packages such as wicd, which makes networking easy without dependency bloat; other distros reap the benefits of it too.
Wicd is proving difficult for 14.2. I must admit that I prefer network-manager because of the convenience of the modem-manager when using a usb mobile Internet dongle.
I take the general point you are making. I'm an end user of Slackware. I think that anyone who has ever successfully installed Windows on a laptop would cope with a Slackware install fine if they read the docs on the DVD. Slackpkg makes updates reasonably easy.
wicd is pretty much obsoleted outside Slackware because of its atrociously slow development pace. connman beats it by far in terms of "easy networking without bloat", and NetworkManager doesn't have noticeable bloat if you have a desktop environment anyway.