“I believe the no assault rule for DS comes from the fact that the vehicle counts as moving cruising speed and we cannot assault out of a vehicle that has moved. The rules just re-state this fact for clarity.”
I also answered this part of the statement as using this definition means that units arriving by
DS that aren't in vehicles can assault which the rules say they can't. You've come up with an unreasonable reason behind a rule with no evidence that also contradicts the rules as you reason why they should be able to assault if the rule didn't specifically prohibit it.
Using your reasoning Scouts can assault out of a DSing Land Speeder Storm it is open topped to the assaulting out of moving vehicle restriction is removed and it doesn't specify that you can't assault. Since the
DS assault restriction is just a reiteration of the vehcile movement restriction according to you they can assault.
Also the Vanguard Heroic intervention rule does nothiing as units DSing with jump packs can assault anyway as they have not disembarked from a vehicle (hence that restriction which you claim is the restriction mention in the DS rules) doesn't apply.
etc etc etc...