I think that it is great! It makes Linux distinct. It is free and open
source, meaning that anyone can change it and that also means that nobody
can own it, It is this that frustrates Microsoft. It is the only competition
that they cannot buy. Instead they choose to subvert by spreading FUD. This
has not had much affect and Linux continues to grow despite their best
efforts.

Yes, there is wasted effort, but not as much as you might expect. The kernel
is centralized and controlled by the Linux Foundation and Linus Torvalds.
There is much more collaboration in Linux than in proprietary efforts such
as Microsoft, which is not as unified as you might expect as one hand does
not know what the other is doing in larger enterprises.

Ubuntu contributes work to the kernel, to Debian from which it comes and to
GNOME. Kubuntu does the same, but contributes work to KDE. Other
distributions also contribute downstream. They keep in touch regularly and
work together as much as possible. Where the duplicated effort is, is mostly
in the distinctness of that distro. Setting release dates, working on
installers, maintaining packages, etc. However, the work is parcelled out so
that nobody duplicates work. One team will maintain the same packages from
release to release. There are specialists who triage bugs and others who fix
them. This all makes for a better release and bugs are generally fixed more
quickly than in a monolithic company like Microsoft.

The one distribution argument is continually brought up by newcomers,
particularly from Windows backgrounds. It is mostly because they have
mistaken preconceptions. Once they are around for awhile they begin to
notice the efficiency of this model.