Actually, if Yishun was under SBST, we wouldn't see so many
feeders... Instead we will see trunks winding around Yishun
interior and passing by Khatib MRT. Just like what we see in
Tampines, Jurong East etc.
(This is not SBST vs SMRT: the two route planning styles have
their own pros and cons)
The problem is, currently there's a Khatib MRT station there
already in operation and much closer to some Yishun south
neighbourhoods, but it has barely any routes that go to the east
side (811 only at St 81, 117 only along the fringes at Ave 1, and
860 only around Ring Rd). Likewise, none of the trunk routes at
Khatib serve the interior on the east side. This is simply an
inefficient deployment of resources! As a result, regions such as
Yishun St 61 and Ave 4, which are much nearer to Khatib MRT
station, do not have a direct bus.
Feeders and intra-towns cannot serve the direct pair of bus
stops at Khatib MRT well, due to there not being a convenient
looping point downroute. It's up to the trunks.
Many other towns do not have a second MRT station, so be it. But
Yishun does, and it's not properly utilized, while there is a
significant crowd at Yishun MRT / Int.