I don't think you get what I meant. The Melbourne (and Sydney)
examples are not relevant as the bus companies are the ones buying
the buses, while the government funds them, which is not disimilar
to how its done under BSEP. This is different from the situation
now in Singapore where LTA is buying buses directly. One would
expect LTA to have consultations with the bus companies regarding
their fleet and future purchases, as the bus companies are the end
users of the buses and are responsible for their maintenance.
We might be referring to the same scheme. 
LTA is now buying buses directly (as Perth does). While it is
okay to listen what bus operators generally have to say and
consider them as an overall group, it is crazy for LTA to bend over
backwards and buy specific model X for operator A, specific model Y
for operator B and specific model Z for operator C for the same
type of bus (e.g. double-decker buses).
I am pointing out how Singapore might end up with Melbourne's
(and Sydney's) situation if purchasing is done in a way as though
the operators are the purchasers. LTA shouldn't be pandering to
individual operators. At least I don't see that happening in Perth.
While PTA WA used to make bad purchases, at least they stick to
their guns.
Let's say that operator A does get their way with getting LTA to
purhcase model X and Y, while rejecting model W. Come 2022 when
operators switch hands for the same parcel contract, can new
operator B then reject model Y and get LTA to buy their own bus
model Z for the same reasons operator A rejected model W?
Operators should not reject buses unless (1) LTA was silly
enough to put a specific model in the contract that the operator
could argue for a significant breach of terms, which means LTA has
effectively tied its own hands or (2) the operator discovered some
major defect with the buses they are about to receive.
If LTA wanted operators to choose their own models then they
should have stuck to the operator purchase and leasing model in
Sydney, Melbourne, Macau and London.