I think atemis are not emphasised enough in the UK. It is only rarely that an instructor seems to discuss 'vital points'. Also I think Aikido (generally) does suffer to some extent from over compliance from uke.
Adrenalin is usually very high during real situations and soft strikes will not even be noticed, let alone distract someone. However harder strikes can open you up for a counter. I know one instructor who was very much into slapping rather than striking. It has several advantages:
- it keeps your hand open to allow you to take the neck/wrist (or eye gouge etc)
- it transfers more inertia to the ukes head (i.e. even through the strike is soft, it tends to push them due to the length of contact)
- it makes a loud noise and is far more distracting than a punch (which you don't generally feel till a lot later)
- it does less damage than a punch.