Have you never played a KEY game before? They're actually all a lot like this, it's just that half the time there's also the "KEY" miracle. Actually, Angel Beats the anime, is written by the same guy who writes all these Key games and he gave it a similar depressing soul crushing ending, but like usual, gave it a 'key miracle' epilogue.
Admitedly, tomoyo after is one of the most depressing endings he's done. Makoto from Kanon had a pretty soul crushingly depressing route too imo, and I believe it's also similar to one of the routes in Air.
Sometimes, it's like this.