Charging in against someone with an AR-15 and some cover is suicide.
It's hard to fault the cops on this one. The 2012 Florida nightclub shooting was a roughly comparable situation - barricaded shooter, substantial firepower, hostage situation.[1] It took three hours to stop that guy, and the cops had to punch a hole in a wall with explosives and an armored vehicle.
[1] https://en.wikipedia.org/wiki/Orlando_nightclub_shooting