>Current view show Kentum languages as more conservative (so not necessarily
>monophyletic), while Satem was a monophyletic branch (k^> palatals),
No. The palatalisation of k' is also explained as a wave phenomenon, only
showing that the satem languages were closer geographically, not that they
were monophyletic. Satem is one of the most over-worked isoglosses; there
are others far more significant that split the IE languages in other ways.
A better way to see the kentum/satem isogloss is to ignore the
palatalisation, and ask what collapses with what. Kentum collapses k and
k'; satem collapses k and kW.
Peter