When you see that SQL access can ruin data and make them invalid, it's usually a strong indicator of an inadequate DB design. (Maybe you did not have a chance to see a good one?)
The pure, normalized models weren't performant enough so you are correct - the design wasn't all roses in the SQL systems. We had largely flattened down some table groups to be able to get data fast enough. But when you hit that point you may have outgrown RDBMS
I'm not saying you can't get one to run fast enough but the ROI starts to decline significantly.
I'm not saying you can't get one to run fast enough but the ROI starts to decline significantly.