Arch is not forgotten...it is INSANE for anyone who has never used Linux before. Think about it. Who are the people who would be needing to use a extremely lightweight distro? People with VERY VERY old computers...people who are able to run Arch care about their computer and likely don't have such an old computer.
Arch is one of the best distros by far but it is also one of the two most complicated and frustrating distros in existence...the only competition it has when it comes to "ripping your hair out" would be Gentoo...though both could easily be lightweight.
For those who have decent computers I would agree that Mint is the best Windows -> Linux conversion distros but it wouldn't work well on a VERY old computer such as a 512mb RAM or less computer.
"Best" is an opinion qualifier. Why is it the best to you? What benefits does it have over other distros that compete in the "Lightweight" realm?
Personally, I like Crunchbang as a concept and for the most part the distro is nice. However, Crunchbang is not "Windows Migrator Friendly". Openbox is not a good DE for people who are coming from Windows for the first time.
Agreed, Peppermint is a better solution for very old computers than Lubuntu. It is based on Lubuntu but it improves the lightweight aspect in many ways. In fact, the size of the ISOs are even 100mb smaller for Peppermint.
The options you provided are rather flawed.
VectorLinux Light is just a DE update for Vector Linux 7.0 which has not been updated in 2 years. Considering how fast development is for Linux in every aspect, it is irresponsible to suggest a Distro that has been dormant for 2 years.
Puppy Linux was a great concept but it is convoluted and confusing since there is both puppylinux.org and puppylinux.com - if that wasn't enough, Barry (PuppyLinux Creator) has said that PuppyLinux official is no longer going to be updated with full releases, it will only be maintained in "maintenance mode". from the PuppyLinux Blog.
Lubuntu is a very good distro but if lightweight is truly an issue there are many other options...with that said Lubuntu is a very good Distro. So this mentioned is not a flaw but not mentioning the lighter distros really is.
You should have mentioned other Lightweight distros like PeppermintOS, AntiXOS, or for the extreme cases Tiny Core.
PeppermintOS is a distro for those who like Lubuntu but want something a little more lightweight. Peppermint is based on Lubuntu but has even more focus on speed and being lightweight.
AntiXOS is designed for computers that have as low as 128MB of RAM...of course this is insanely small. AntiXOS downloadable ISOs come as small as 140mb with many different DE options such as IceWM, Fluxbox, JWM, etc.
Tiny Core Linux is by far the smallest/lightest distro available. The recommended ISO file is only 15MB with the largest version with all the bells and whistles is only 72MB. Tiny Core recommends nothing lower than 128MB of RAM for best performance but it will actually work on computers with as low as 46MB of RAM.