This kind of comparison has no value. One is multi-user and multitasking, while the other is single-user and single-tasking, so DOS has a huge advantage when comparing stability, or you could say stability isn't really much of an issue for DOS in the first place.
As for kernel size, that is also affected by functionality. DOS is naturally very weak in networking; DOS only includes a few general drivers, while UNIX-like systems usually put drivers into the kernel (that's what I've heard ^_^) so naturally the kernel will be larger, but hardware utilization is better. The same goes for file systems: LINUX supports many kinds of file systems, while DOS only supports a few of MS's. If you add those functions to DOS and then compare size, only then can you say the comparison is being made on the same level.
Actually both systems have their own strengths, or rather, they just can't be directly compared.