I know it has been a long time since I have posted the solution, but let me explain. The reason why the indev versions don't work is the launcher is trying pull the versions and assets from a minecraft webpage that has since been removed. What the solution does is it redirects the launcher to a website that does have the versions and the assets. There are a few updates to this solution. 1. The website has been changed from betacraft.ovh to betacraft.pl 2. About your question, "What would condone removing -Xmx?" The answer is nothing. You don't have to remove -Xmx2G. How long this has been, I have no idea, but you don't have to remove -Xmx2G.
I have had the same problem. But here is a step by step way of fixing this issue.
Open Minecraft Launcher
Go into installations
Click on the three dots icon on the indev version you want to play
Click more options
Go into JVM arguments and remove -Xmx2G
Type -Dhttp.proxyHost=betacraft.ovh -Djava.util.arrays.useLegacyMergeSort=true into the JVM arguments
Save
Now you can play Minecraft Indev.
I think I will create another report on the signs attaching to other signs bug.