The gasket design was a big part of it. There were apparently incompatible materials, that in the infancy of employing this stuff, they didnt realize yet.
Some vehicles had a radiator neck and cap that wasnt great for using Dexcool. It would allow some sort of seepage and/or air entry, which was not good for the coolant. My truck has this 45 degree radiator fill, but Ive not had issues. The recommendation early on was to use a metal Stant cap instead of the plastic GM one. Youll note that newer engine and coolant system designs often have a pressurized overflow bottle, which avoids these issues altogether.
The other major issue was when silicated antifreeze was added as a "top up". These are incompatible, and tend to cause the silicates to drop out and create a gel that is a pain to remove and clean. This was a concern especially early on, when shops that provided free top ups with service would pour whatever they had in there, sometimes mixing chemistries.
Overall, especially at this point, there are billions of miles of experience with dex, and lots of high mileage examples of vehicles that lived their whole life with Dex. These legacy engines were problemmatic because of both design, materials, and user error at a time when the situation was changing. That's long past.
If your dex looks good, if the radiator looks clean, and you dont have any evidence of leaks into the engine/oil, Id keep running Dex. Its a pain to change over chemistries, and takes a lot of flushing and coolant wasted. If you suspect an issue, do it as a best practice. Otherwise, keep with Dex. Its cheap and ubiquitous.