Although I agree with most about the premise of an RTS game being very complex - if the guy is dedicated he can make it happen, even without programming. The extreme difficult part beyond the complexity of the genre will be any type of networking desired. Not easy without knowing how to code.
That said - don’t be dissuaded on your quest - we all have to learn our own way, even if that way might be the hard way. 
And check out some of the quality products created using Playmaker
WIP Cryptarium (Dark Dungeon) page-4#post-3223897
PlayMaker - Visual Scripting for Unity page-48#post-3226521
Also might consider other visual scripting solutions available on the store, some more robust than others.
Good luck on your journey.