To throw in my credentials, 41 years flying single and twin engine jets and only the last was not cleared for formation landings. A basic flying skill taught to, and practiced by, all fighter pilots world wide.
Yes a formation landing may be dangerous if the "Swiss Cheese" holes are aligned. Being taught and adhering to the correct techniques will always reduce the risks. There are many reasons why for nearly 100 years we have flown formation landings.
Like many aspects in aviation, it is often more than one factor that will lead to an accident. Example, a flight lead who flies the approach too fast "to help the wing man". The flight lead who lands long and flares very slowly "to help the wingman". The instructor teaches the wrong technique because "he knows better", all may contribute. There is no doubt that an inexperienced wing man using the correct techniques can be led by a good flight lead to a successful formation landing under most conditions, but always something MAY go wrong.
If things go wrong it is as much down to luck as good skills to walk away without incident. Any BOI that dissects the information AFTER the event and concentrates on minutiae is wrong.
BV, yes your correct that the USAF employs IPs to instruct their student pilots. Don't, however, imply that QFIs are necessarily any more capable that IPs. I have flown with some very talented IPs and some cr*p QFIs. There were a few techniques that I learnt from the USAF whilst flying the F4 that were never taught on our RAF OCU. Equally, I would like to think that we (the RAF) taught our USAF counterparts a few things that they had not seen previously. The only problem being that the USAF is too large an organisation to effect change easily.