Accounts are the correct level to separate these at. Keeps credentials easier to manage for devs, techs, etc, and limits blast radius if unauthorized accesses take place.

I work with both style of AWS installations. Having organization is a constant pain for people who access multiple accounts even with something like Okta. 1 browser can access 1 account and if you switch you have to go through the switching process, or use multiple browsers. Quite often people would like to access cross account resources which a whole different level of discomfort. This is why I still think, old school or not, that having a single account and multiple VPCs is a better option.