You described a specific network problem, but suddenly there are “so many”. That might be the case, but it doesn’t help anyone here.
Moreover, advising other people (with “similar” problems - whatever that actually means) to rely on the return policy and simply send the device back instead of working on a solution is very questionable.
These issues with RB5009 are not unknown.
Have you tried disabling HW offload?
http://forum.mikrotik.com/t/rb5009-2-5gbe-problems/169157/21
There are people showing speedtest results with confirmed 2,4gbit in both directions.
https://www.reddit.com/r/mikrotik/comments/1bpzj2o/comment/kwzw1ke/
As far as I know, it’s a buffering issue with the switch chip. In any case, it helps if you use the RB5009 as a router on a stick. Use the 2.5Gbit port for your WAN and connect a 2.5Gbit switch to the SFP+. Your bottleneck is resolved.
Like here, a CRS310-8G+2S+IN would be a good match.
http://forum.mikrotik.com/t/rb5009-and-2gb-s-internet-speed/176055/10