Disappointing 2.4 speeds

So here's what I did to test the issue: I made some speed tests with the EX6200 on the 2.4 GHz frequency (screenshots attached, prefixed with EX6200), and then turned off the EX6200 2.4 GHz radio, attached my trusty old Linksys E4200 (v. 1) to one of EX6200's wired ports, and turned on E4200 2.4 GHz access point. In effect, I replaced EX6200's 2.4 GHz radio with E4200's (same channel, same settings). I then made some speed tests with this setup--see screenshots prefixed with E4200. I need to stress that these results are pretty characteristic of the two setups. As it can be seen, the difference is pretty shocking. The only explanation I have so far is that EX6200's 2.4 drivers are half baked (assuming, that is, that the issue does not reside in the hardware, which I am hoping it is not the case).