"And which USA drug are you talking about that would be the...

"And which USA drug are you talking about that would be the immediate competition for PBT2 that would prompt a massive investment in getting FDA to hold us up?"
In my opinion and experience, I do not believe it is any ONE drug, but the numerous drugs being used to treat AD at present. All are unfortunately only palliative. Drugs are used to sedate, decrease anxiety, control restlessness etc. etc. My experience tells me that it must be a multi million dollar market.
The drugs used are changed as the disease progresses. The patient eventually becomes unresponsive, is given morphine and dies.
In the case of my relative, she lived about 15 years after diagnosis, so probably went through many kg's of drugs at great expense with no benefit to her. Sadly, in the early stages, she would have taken her own life had she been able.
The culprits here are many and IMO, collectively have the ear of the FDA.