OK. The issue is that the mobile app isn’t really a very good UI for controlling your lights day to day. It really is a configuration tool more than anything else. It’s where you set things up.
What you need to do is figure out how you really want to use your Smart Things. For example, there is a community published SmartApp called Dim and Dimmer. You create a Virtual Dimmer in the IDE; this will show up in your Things just like any other dimmer, and you could put it in the same Lights & Switches group. Then you install Dim and Dimmer, using this virtual dimmer as the master, and your real dimmers as the slaves. Whenever you change the dimLevel on the master, all of the slaves follow suit. That gets you half way to your goal.
Then, you install ActiON dashboard. That virtual dimmer can show up there, and that makes adjusting it (and all of the real dimmers) very easy on a single page UI. ActiON gives you a very clean and simple web interface to your ST setup.
If you really want to make the most out of SmartThings, you will need to do things like this.