I dunno, I kind of have to agree with that point. Since their goal is to have everything feel like Half-Life 2 they're spending a lot of time reinventing the wheel to replicate what Source does out of the box (down to the physics bugs in the locomotion
) which is taking a lot of time away from them actually making improvements.
Boreal Alyph is on Source and while they're also in a very early stage being on Source means their time has been spent on updating the engine and making the gameplay feel better rather than doing stuff like trying to replicate HL2's (kind of dull) gunplay. You could easily make the valid argument that once the core stuff is finished Project Borealis' team will have an easier time making new content because they're not bogged down by Source's clunky pipeline, but until they're done with that there's not a whole lot they can work on gameplay-wise. Some of the stuff PB has shown off looks very
promising but they're devoting far too many resources on stuff that's already been done in Source.