He had a high caliber weapon, a super duper gun - it was simultaneously the gun being taken and ice shooting, how was ice supposed to know he wasn't reaching for another weapon or the exact one that was being removed from him, they were protecting the ice agents as they should of been
They had Alex incapacitated and on the ground, the next step would be searching him for weapons (that's if he was in any way aggressive before they tackled him which he was not). If the agents in your scenario were unable to properly search Alex and then properly communicate among themselves that he got disarmed, then they were incompetent on the most basic level. Literally more incompetent that any policeman fresh out of training.