IIRC, there are other important factors like AES acceleration which is available in the RB5009 and not on the RB4011.
RB5009 is known to be able to drive more than 400mbps of traffic via ZeroTier with ease. So, it is not about lust for new gear.
Also, RB4011 vs RB5009 benchmarks are not comparable, given that RB4011 results were achieved using ROS6 and RB5009 using ROS7. The underlying changes are considerable and there has been a lot of debate around those metrics.