Sheer guesswork from what I have heard:

Presumably the inside people had at least someone outside, perhaps with cel fone or other - for advance warning of something as obvious as.. 50 ambulances. Thus their arrival would certainly risk.. element of surprise. Now why they weren't positioned a mile or so away and dispersed - may be a valid criticism.

(No I have no explanation of the way the commandos were assembled invisibly, but must presume this is Tactics 101A and they were not singing marching songs)

Otherwise, from what I've heard recently of the putative composition of the gas: one substance used as an antidote to certain alkaloids.. another component a pharm-chem substance alleged 1000x more potent than morphine - seems likely they would have had little experience of using this on a significant number of civilians; little data to suggest exact dosages. Obv. they neded to incapacitate the human bombs or risk total destruction of the building + occupants + their own troops.

So I concur: Putin did the best he could manage - pending any weird shit that next surfaces.

Ashton