We will indeed never know the actual extent of the faults of Impulse 2 motors. Neither Kalkhoff or 50 Cycles would admit that it's a widespread issue, due to the related liability. I guess it could also depend on usage. Maybe people cycling at 10mph for 2 hours each week-end on flat paths will never have an issue.
If only a couple of people were complaining about motor failures, then yes, it could be seen as being partial. However, feel free to search on Google on German, French or Dutch websites for other user stories, or on this forum.
Also, I believe the issue is probably under-representated online, due to the typical profile of a Kalkhoff buyer (won't be a 20-year old, with no disposable income, which would be more likely to be vocal online).
If the motor replacements were fixing issues, then it would be less of an inconvenience, but several people (including me) had also failures on new replacement motors, meaning that the issue has not been resolved by the manufacturer.
If your motor does fail at some point, and you experience the "unique" aftersale service from 50 Cycles, I am sure your perception and recommendation on Kalkhoff would change.
Even if the replacement/refurbishment in or out of warranty is free, there is still inconvenience to bring the bike back to the shop, be without a bike for days or weeks, and/or be stranded miles from home without assistance, riding back home on a 25kg bike.