And I always thought there's no depth of field at all with compact cameras
There is always a "depth of field", but the smaller the camera the bigger it becomes for a given aperture - hence the reason why single use cameras can get away with no focussing system at all - at a small aperture on a very small camera the DOF is from a few feet to infinity.

If you have an X700 you're good to go for any eventuality.

managed to shoot on ISO800 which I think is the reason they were so awfully grainy
If you shot 200 film on an 800 setting, the film lab would have still tried to get an image even though the negs were significantly underexposed. Flat, grainy images would definitely be the result!

Lots of recommendations here for other labs. Not saying boots or whatever are bad, but I think you have more chance of consistent quality using one of the mail order companies. It does seem that high street labs are getting a bit variable depending on who is operating and how well they are maintaining the kit.