As RTS and Minecraft player I must say that Starmade is very easy.
Yea, i'd somewhat agree with this. As a game, the skill cap isn't mechanically high like Starcraft or Dota for example. However it takes time and patience. Some players like instant gratification, which is not something starmade offers in the first 20 minutes as of yet.
The main problem lies with how immediately accessible Starmade is to a new player. I think the first 20 minutes can be tricky to understand for a variety of reasons and subsequently put off new players that are not already a fan of / or understand voxel games.
The features are squashed into a placeholder UI, which can be really confusing. The tutorial and starting 20 minutes could be more dynamic and the missions / narrative are still in the making. So unless you love the free roaming "i can build anything!!" feeling, it could be a strange experience.
The good news is, the dev team know all this, and are working on it almost daily. They have plans they want to explore to make Starmade even easier to pick up and play and be engaging from the first few minutes. Hopefully your friends will enjoy the game further along in development.