Don't agree that they'd be faster, people slide down 2 at a time much faster than trying to stumble run down stairs.......I can just imagine the people falling over themselves trying to run down steps!!
If the Fire is contained/out and the threat is known by all means use those stairs, if the Fire is not under control then keep those stairs AWAY from my Aircraft as I'll be using the certified slides that came with my $200 million dollar Jet thanks all the same.
As an operator that frequently flies into WSSS I've never been informed by anyone that they have stairs they'd like me to use and not my slides in an EVAC.
EMER EVAC required, SLIDES.
PRECAUTIONARY DISEMARKATION required, by all means use those wonderful stairs.