Hi PharmaG, wow, you have been in a very long admin phase. We have been in ours since November 2017, and may not start building until December/January.... and I am extremely frustrated at the slowness we are currently experiencing with M. However, from all those that I am following on this forum, many experience this, but have relatively good build experiences. I don't really believe any of the volume builders differ from each other too much. If you look up reviews for other builders you will see the same. Remember, most people take the time to go online and offer an opinion when they are pi$$ed off with an experience - not so much when they have a great experience. I am sure there are many people exceptionally happy with their M build.
It also comes down to the tradies that are on your build - all are subcontracted and this can give you a very different experience to the next person building with M. Same goes with the Site Supervisor/Manager. They make all the difference. You have done the hard yards so far, so hang in there. I am sure your build will go well - just make sure you stay involved and across every stage of the build. Even better, get an Independent Inspector to check every stage for you. This will keep M on the straight and narrow