Agree with Greg, no one fw sb can be too deep. For a few courses, heck, they can all be deep. For most courses, the generalized theory is that fw sb can get deeper as they get closer to the green, with the basic goal (hard to be consistent with free form shapes) of being just deep enough and with appropriate slopes, to make escape a 2/3 likely to succeed, but requiring a good full shot.
I believe par 5 sand bunkers in the first LZ can be really deep. Even if you only hit a 9 iron out, you can still reach the green so there really isn't even a penalty, unless you think it is your right to hit a par 5 green in 2.
I once told a shaper who asked how deep the fw bunkers should be to figure out what club golfers would be hitting out, and make the bunker that deep, i.e. 7 feet deep for a 7 iron shot (I told him to figure conservatively using average golfers and 150 yards as a guide for 7 irons, not pro tour golfers who would hit a wedge out, LOL. Nothing exact, but it conveyed the idea to at least one shaper.
I once lost a job when this question came up. My answer to , "Mr. Brauer, don't you think it should be just as easy to hit the green on a par 5 hole from the bunker as the middle of the fw?" didn't seem to please those members.