The beauty of Minecraft is that it's an open-ended game. YOU decide what your style play is and what you want your challenges to be. Anything can be legit as long as you're having fun.
I could easily say that automated mob farms are not legit because it's a cheap way to gain XP without actually fighting, but I will resist the temptation. To each it's own. I admit, I use X-ray, because I just don't enjoy digging forever and ever. I rather use my precious time on creative projects and developing tactical advantages against evil mobs.