The whole idea that kid sidekicks are an 'indefensible idea' is just a silly one, regardless of the era. That was a solid genre convention up until the Eighties, and even then it took until the Nineties to really kill it at DC.
If you judge solely by DC, you might think a lot of outdated concepts are still viable, from kid sidekicks to superpowered pets. The fact is, the concept has essentially been dead in the water since Stan Lee modernized the industry in the early 60s, along with a lot of others. DC just took a while to catch up, and then in the last decade or so went retro again.