I think one of the main reasons for the necessity for defense is the prevalence of electrification. Electrification is easily defeated with defense, but significantly less so without it. Another major factor, of course, is how without regeneration higher lifeforms must travel back to the hive for healing, which greatly reduces their time spent fighting. Both of these factors can be overcome to an extent with the use of permanent supporting Gorges, but I find that these are a rare sight.
I am willing, however, to try out other chamber orders, as long as it is understood by the team that a greater amount of teamplay and coordination will be necessary.