How do you know I do not have the qualifications to drive the aircraft?
Sorry, but it's pretty obvious.
Is there even a single example which can be provided where, because a crew with stuffed-up results on their record were given a heavy sanction rather than a milder one, safety inquiry and system improvement suffered, even suffered at all?
Unfortunately there are many.
E.g., the "most severe" sanctions, to borrow your words, would be criminal ones. As such, in many countries accident investigations fall into purview of the criminal justice system, along with very strict rules of evidence, etc., required by that system. Yet this focus to "criminalize" pilot conduct has had an impact to safety:
1. After the ValuJet crash in the everglades, employees of ValuJet's maintenance company SabreTech were charged in Florida with 110 counts of 3rd degree murder and 110 counts of manslaughter -- one for each crash victim. A few years later, when the NTSB investigated the 1999 pipeline rupture in Bellingham, everyone "lawyered up". And worse, prosecutors prevented the NTSB from doing their job. Statement from NTSB Chairman Jim Hall at the time:
"The NTSB wants the answers to all of these questions, and we need to know them as soon as feasible. But, my investigators have been stymied by the prospect of criminal prosecutions . . . A number of our investigative activities has been suspended because most of the central players will not talk to us. And, prosecutors have asked that we not test the valve of the pipeline until their concerns regarding evidence preservation can be allayed. "
2. In 2009, a Cessna Citation crashed near Rome. The judicial authorities immediately seized the CVR & FDR and
refused to release them to the Italian Transportation Safety Board (ANSV), for months!
3. Similarly after the XL Airways / Air New Zealand A320 crash in the Mediterranean sea, French judicial investigators took custody of the FDR and interfered with the safety investigation, preventing the damaged FDR from being sent to the US for read out at the manufacturer (Honeywell) until a compromise was found.
4. Indonesian authorities wanted to "send a message" after the Garuda Flight 200 crash in Yogyakarta by criminally sentencing the Captain and sending him to jail. Afterwards, dozens of the Indonesia's most senior pilots and ATCO left to other countries rather than work in an environment where there's constant fear of criminal prosecution. If anything, the country's safety situation only worsened further.
5. I recall at least one case where the CVR was lost to fire because judicial investigators refused to give timely access to safety investigators who wanted to secure the blackboxes in the aftermath of a crash.
These are inevitable consequences from the urge to "throw the book" and impose "severe sanctions" for
unintended operational errors.
Criminal prosecutions are warranted in cases of where there's
willful violations of the law. Otherwise, pilots, mechanics, ATCO, everyone else involved in aviation will simply "plead the fifth" on any incident or accident. There will be no self-reporting and coverups will become the norm. Safety will greatly suffer.