I'd argue that chess similarly has "useless skills". But learning "useless skills" is one of the most important things you can do for yourself to learn "useful skills".

Not everything has to be an absolute competition-or-not. For the same reason you can enjoy a casual game of chess with a friend, you can enjoy a casual game of some RTS. Helps that there are a lot of open source RTS communities that each have their own skills-emphasis.