Indeed SBST 158 has been downgraded, over the years !!!!
Used to be 100% M-B O 405 then the Volvo B10M took over, with their
vastly inferior suspension ride comfort especially over the
underground line construction areas along Paya Lebar Road, where
one's backside gets tossed like hell, with hard jolts thru the
spine !! From O 405 to B10M, of course it's an (uncalled for)
downgrade, no doubts about it !
Fortunately there's still some O 405 deployed on SBST 28, so that
there's still a superior class of travel even @ higher speed over
those stretches of lousy roads !