These guys blew themselves up after they were cornered by the police. It would be possible to shoot them before they could reach their detonator.
The most deadly thing is VBIED’s (vehicle bombs). The second is large suicide vests where the terrorists places himself with a crowd in front of him and detonates.
I have carried for over 20 years and there is no doubt a firearm can be used to minimize a mass shooting or idiot with a knife, but look at the history of Israel. The most effective attacks have generally involved explosives and they are the hardest to stop.
Again, denying jihad Johnny access to the target via immigration is the most foolproof way of preventing this. I don’t take anything away from the 2nd Amendment, but our focus must be on defensive immigration policies.