I've been pondering a proper reply to this thread without writing a book...
I agree, RC Lipo has the most potential for a dramatic release of energy compared to lower power cells when things go seriously wrong. It all comes down to the user, knowing enough about batteries to spot a problem before it turns into an accident.
A pack is only as good as it's weakest cell, in a perfect world, all cells would be equal and die at the same time after a specific number of cycles or calendar months/years, they do not.
I have built dozens of ebikes for friends and customers, depending on each person's level of understanding, i've set them up with what was best suited to their needs... for some .. it's money.. for others it's reliability.. and everything in between. That being said, i have met and dealt with some people who simply do not have the required diligence to own anything but a completely protected battery pack to protect them from themselves... ( the things some people will do.... oh man... i worked 16 years in a call center doing Tech Support.... i could write a book. ) ... and .. there are also some very intelligent people out there who " get it " and understand regular common sense, with enough education they can operate a high power, high voltage, dangerous ebike as well as myself and many other 1%'ers ...
Got a big box of BMS's, from all sorts of suppliers, large majority of them suck, however there are finally now some passable units, but i have spent / wasted 1000's of dollars looking for the one " Perfect BMS " .. and it's not here yet... at least not an affordable one.
Building a pack with " End of Life " recycled cells, is stacking all the odds against yourself from the starting line.... yes it's possible.. no it's not a good idea, for all the reasons i have listed already.