This inequality is not enough for me. You have to nullify my argument of Post-23 with convincing statements.
Without Bootloader, we can't upload the sketch and also we can't jump to the execution point of the sketch in the application flash. So, it is working like a ROM-resident Monitor Program (one kind of OS) of a Microprocessor Trainer like ETW-6802/SDK-85 which has both Keyboard and Monitor.