The cool part about this game is that my first impression was the same as yours (wtf backwards?) and there are a few knowledgeable people in here (in this thread, no less) who were able to shed light on this.
Here is a video of a square rigger tacking:
https://www.youtube.com/watch?v=BxCKGS_bLKI
Another good source for noobs like me (if you ignore the terrible music)
https://www.youtube.com/watch?v=v6DZIvMZWzQ
It would be cool if we had different wind speeds and not perpetually perfect conditions (and full sails at all times) so you'd need to keep a watchful eye on your sails.
I also agree that, against the AI, sailing backwards is silly but can be effective. It's less of an issue against players who know their trait.
You are also right about your other point: there isn't enough crew to fight both sides at full efficiency in RL.
We'll see where the devs strike the balance between realism and playability I guess.