It was a trade-off for a very long time (late 1960s to late 1990s IMO): the output of the early compilers was much less efficient than hand writing assembly language but it enabled less skilled programmers to produce working programs. Compilers pulled ahead when eventually processor ISAs evolved to optimize executing compiler generated code (e.g. the CISC -> RISC transition) and optimizing compilers became practical because of more powerful hardware. It definitely was not an overnight transformation.