No, GUE doesn't use sidemount -- and there is no question that there is some exploration diving that is not possible in backmount. But the vast majority of folks diving anywhere are not going to do those dives.
DIR isn't the only way to dive. It isn't even the only good way to dive. But it is a very good way to dive, with a lot of advantages, including the ability to slot into a team anywhere in the world and feel immediately at home, because the standardized gear and protocols makes everything very easy.
DIR isn't the only way to dive. It isn't even the only good way to dive. But it is a very good way to dive, with a lot of advantages, including the ability to slot into a team anywhere in the world and feel immediately at home, because the standardized gear and protocols makes everything very easy.