I think it was advised a bit too early, but ever since flexbox entered the scene, tables for page formatting became irrelevant.
And just in case, nobody ever said tables were dead. Tables were declared bad practice for page formatting, not for tabular data.
Even for layout, CSS took a long time to catch up with tables in some areas. Tables were not designed for layout, but there's a lot of aspects to them which are easier to grasp and work with than trying to get the same effect with early CSS.
Do not use flexbox for page layout. It invites nested flexboxes, which eats your reflow performance.
Use grid instead.