I don’t want to defend police violence, but knockout gas and tranquilizer darts are more of a Hollywood trope than actual viable method of subduing combatants.

Example: https://en.m.wikipedia.org/wiki/Moscow_theater_hostage_crisis

The important questions to consider aren’t how to make police violence less lethal but to consider if police needed a heavy response to begin with.

None of those are realistic options. Gas has to be administered by an anesthesiologist to be effective (else you get this), tranquilizers also have to be dosed and probably aren't very effective on an armored target behind cover, and there's no way to shoot someone just to wound like in the movies, since even a shot to the leg could sever the femoral artery and cause someone to bleed to death very quickly.

I agree that this was probably disproportionate, but I'm not sure what other option there is in the short term when the target is an armed and fortified paramilitary force.