In my opinion, 961 needed DDs. I'm not sure about full-day and
weekends but weekdays peak hours definitely needed a few. I used to
take service 961 between Woodlands and Queensway a few years
back.
During AM peak buses leaving Woodlands were packed door-to-door
from Kranji station onwards and at Kranji, there were always people
who couldn't board.
During PM peak buses arriving at Queensway towards Woodlands
were packed door-to-door too. I could still board but from the stop
opposite MDIS onwards the bus was completely packed (usually got a
batch 1 MAN A22 at that time) and there were some people who
couldn't board at some of the stops.
That said, that was when the fleet was a mix of O405s and MAN
A22s. Maybe more recently just prior to the introduction of DDs it
was different.
Yes also have to consider between few years back and now there
has been quite a few fleet add to the service. 961 used to operate
with 26 buses, now operates with 32 buses in the last 3
years.
Having said it, 961 is such a long route that by the time it
starts in peak in one part of the country, it is already off-peak
by the time it reaches Bukit Merah region. Mandai estate is the
reason why 961 is still packed in AM at Kranji but there is
160/170/178/960 to complement as well. Really depends on who comes
first.