A crash is not the only negative result of bad workmanship (but, no, I am not aware of any accident that could be attributed to excessively deep countersinks).
What overly deep countersinks are likely to cause is a progressive degradation in a structure that would be first detected by smoking rivets.
Even if that is the only negative result, that is a reason that a builder will be advised (what they do with that advice is up to them) to replace a major structural member that has been severely over countersunk....... If they are told it is fine, and then 500 hrs of flight time later there is a lot of smoking rivets, the typical response now a days is for the builder to look for someone else to blame. Who do you suppose that will be?
Diving a bit deeper......
Keep in mind how a riveted joint works.
The primary load orientation of a rivet fastener, as used in aircraft design, is a single shear joint.
The simplest example of this would be two overlapping aluminum sheets joined with an AN470 rivet. Any load applied that would try and move one sheet away from the other is trying to "shear" the rivet across its diameter via the edges of the hole in each sheet, baring against the rivet shank.
With that in mind, look at the 3rd photo in
THIS POST I made previously, were the countersink is only .004" over sized beyond what is recommended. Note that there is nothing for the dimpled sheet to bare directly against, until it moves enough that the lower face of the dimple comes into contact with the wall of the countersink. The rivet would take some load prior to that, but is purely in bending so it wont resist movement very well.
Detecting a .004" difference by evaluating the fit of a test patch dimple is very difficult. Especially since there is a large variation in dimple quality because of different dimple dies, tools used, and technique in using them.
There are already many posts in the forums that have pointed out that bottom shape of even the best dimple doesn't match the shape of a countersink. For this reason, making a test sample and countersinking for it to fit perfection flush with the surface that is countersunk
will result in a dimple that fits loosely in the countersink (and usually worse than the .004 over sized example in the photo).
Wrapping up -
It is frustrating to us, to see single builders pushing specific build advice (based on their personal build experience, often on an airplane that hasn't yet accumulated very many flight hrs) that is contrary to recommendations that we make that are based on actual in depth testing (such as the rivet samples shown in the photos of the post I linked too. This is home building after all, so every one is free to choose. My suggestion is to do your research, and make sure you understand all of the factors and variables involved with a particular detail, before you choose.