I'll bite.
I'm guessing they're referring to the abundance of bosses / endgame fight mechanics relying on scripted move sets instead of an open available move pool.
This leads to Youtube videos becoming more like manuals for fights in the sense that they boil down to "Do this at X time, at X% HP, dodge this at X time and it will always be followed by X move" as opposed to actual guides that would function more like "The boss has the ability to do X move so be aware if it happens"
This trend has led more to players learning the "script" of most fights as opposed to learning how to properly deal with varying and changing mechanics.
The reason they have gone this route however is most likely an attempt to boost the overall success rate of the DF, allowing players to learn a script probably yields better results within the time limit due to the random player environment that the DF is based around, as opposed to putting the stress on players to grow accustomed to a wider range of mechanics.
Ideally they could have solved this issue by making guildhests both mandatory as part of the main scenario and worthwhile by steadily introducing players to various types of boss mechanics that they might come across in future content.