Well, that depends on how we're defining 'skill' in warfare. It gets kinda complicated, see. More can always be said on the matter, so if anyone would like to explicate further on Sparta and how good they were at warfare, please don't let this post stop you!

For the meantime, you may be interested in u/Iphikrates' thorough breakdown of Spartan proficiency and why they have their image, and I highly commend the good Doctor's flaired user profile if you want to know more than you ever thought you'd want to know about Classical Greek warfare.