I cannot answer your dban question, but I can answer the one involving DOS. The problem with DOS is that it no longer supports modern hardware. It does not understand SATA. It does not understand logical block addressing (LBA) as it used CHS (Cylinder/Head/Sector). The basic capabilities of DOS to handle large disks stopped at 132Gb - it was only through Bios extensions and in some cases an increase in disk controllers from 32 bit to 48 bit addressing capability that allowed this limit to be overcome to some degree. There is also no realistic USB support, no support for UEFI bioses and no support for GPT file systems. Unfortunately, support for all these modern innovations means that a more comprehensive disk operating system is required.
Microsoft, in their infinite wisdom, decided it was a lot easier to develop and maintain a "DOS-like" boot environment by taking their current windows operating system and removing the GUI bits, leaving just the command line parts. Sure, it's a couple of orders of magnitude bigger than DOS but the support for different hard disk chipsets and different NIC chipsets is a lot simpler to implement. You can also build boot media on USB sticks, USB drives and optical disks as well as booting over the network. Although it may take a bit longer to boot, the overall performance gain ultimately saves you time.