When RDA held the 155 lb UFC belt, he passed out cutting weight.
Moving up to 170 solved weight cut issues but he had no answer to wrestling bigger & heavier opponents, who knew how to use their reach advantage.
RDA's kickboxing might have been at its peak under Rafael Cordeiro at Kings MMA. That weird thing happened with someone in that gym accusing RDA of steroid use. RDA left kings MMA for evolve MMA and bounced around between different gyms. Leaving california and ending up in brazil.
RDA fought all of the toughest guys he could get his hands on. Lots of respect to him for that.
For whatever reason he had trouble with the 155 weight cut and fought a division up, lost his best coaches and had trouble replacing them.
He may have just gone through a natural transformation of some sort not related to USADA. It's not like it was proven that he was a cheater unlike Vitor Belfort who we knew cheated and as a result had to keep cheating with TRT and when he had to stop he stopped being relevant once again.