No buffer-bloat issues here, considering I was getting an F before turning on StreamBoost QoS and setting device priorities, after which I would get an A and occasionally a B. Adaptive QoS's recent updates from Broadcom has gotten better I will admit, as the R8500 does get better bufferbloat scores but its not night and day.
You have to set QoS bandwidth limits manually and set the speeds to average that you get, not the max, that maybe your problem. When I was on CenturyLink I would get 36-37/4.5-5 Mbps so I set limits to 34/4 Mbps and got an A on DSL reports speed test. Recently I switched to Comcast and even without QoS now I get a B on average on both routers (R8500/R7800). The third router of mine, an R7800 on LEDE/OpenWRT with Cake QoS which in a way is a successor to FQ-Codel (same people made that) is probably the best Bufferbloat wise.