Everything is a compromise.
No one weapon system configuration you pick is going to be best at every situation you will encounter. SOF or otherwise.
I personally don't have military experience. But its clear that 10-12" ar15's have their place, operationally. I personally have a friend who was army SOF and then went on to work for "the agency", in 40+ deployments around the globe - almost all with 10-12" barrel ar-15 systems. It worked very well for him and his purposes.
It all comes down to what you want to achieve, and what tradeoffs you are willing to make. In some situations, a 20" barrel ar15 will be optimal or suitable. In others, a 10.3" barrel. Others, 14-16". It's all a compromise. Arguing that one barrel length is better in all situations, or that barrel lengths less than 20" are less reliable is idiotic.