On the contrary, my experience is that PLD downsyncs better because low-level dungeons have more interesting tanking tasks (e.g.: you can use Shield Bash as a chain-stun to attempt some truly enormous pulls in ARR dungeons), whereas BRD downsyncs like crap because, as a DPS, it can only do DPS and BRD's level 50 kit, specifically, isn't fun. With PLD, the poor kit matters less because you can supplement it with a lot of content-specific optimizations that make use of the higher skill ceiling on early dungeons.