As you can clearly see in your own link, accepted answer is not the most popular. For some reason authors wanted to avoid application plugin and it is just not reasonable. Application plugin not only adds main class to manifest, but also creates a few very useful tasks. If one is keen on using the system not the way it is supposed to be used, no amount of documentation will help.
I recommend to use gradle tasks instead of IDEA build system wherever it is possible. Luckily, IDEA allows to do it very easily (just open gradle sidebar and select a task you want). You can event configure IDEA to always use gradle instead of internal build system, but it does not always work as expected.