It's more like the DIA isn't a fan of logic, fact, reason and reality.
Perhaps PLA feels MIRVs are susceptible to advancements in mid-course interception (resulting in interception of delivery vehicles prior to MIRV separation and dispersal)?
Think of it this way, the old PLARF doctrine saw MIRVs as a way to saturate enemy missile defenses. However, this also means that a first strike from the US may destroy multiple warheads in one hit (if the warheads have been loaded onto the missiles, as per PLARF doctrine during emergencies). This means that warhead survivability may actually decrease if the enemy launches a first strike.
Even before MIRVs separation and dispersal it's not particularly more vulnerable than 1 single warhead in that same spot would be. I don't really think this is the reason for the PLA not using MIRVs more.
A single warhead being intercepted results in loss of one warhead, whereas a MIRV being intercepted pripor to separation and dispersal results in loss of multiple warheads.
I believe he means HGVs, for which we have very little information. HGVs are much more difficult to intercept for obvious reasons, hence vastly increasing the probability of the warhead reaching the target.
True but there are a lot of other considerations. After separation it's harder to intercept MIRV. Further MIRV are inherently a better usage of throw weight than 1 big warhead because of the general smaller warheads are more efficient thing. Also depending on where the separation takes place it can be pretty hard to intercept before it happens. Finally, given the low success rate in intercepting ICBM warheads in general right now and the fact that so few interceptors are available I don't think this is the major consideration on MIRV vs single warhead.
I suppose it depends on the relative cost of these things and strategic doctrine. I don't think a warhead would cost more than the rocket to procure but it is possible PLA doctrine wants more control/less of them around given their no first use policy and general conservatism in this field.