Nothing I can do I’m afraid as a lowly customer but I suspect this boils down to a realistic flow rate for a single controller at LLFIN within the confines of the sim.
In the real world if Heathrow director gets backed up with traffic then the approach controllers would fill the holds (LAM, BNN, OCK, BIG) and then subsequent outer holds would be used. Realistically flow rates could then be adjusted and slots issued, which in the sim isn’t possible, so if a sector becomes overloaded at a particular time the best course of action would be to try again with a lower flow rate.
There’s a reason AI will never take over real-world human beings and it is simply because it’s not as good and never will be!