USB 2.0 Wifi speed halved? (Lamobo r1 and RT5572 module)


I also tried (and failed) create cheap+ultimate router/nas combo.
My choice of hardware wasn't the luckiest one, but, it's working, after desoldering and changing crap original usb wifi module with this

using rt2800usb driver with latest rt2870.bin

The problem is, it's working good, until I found, my wifi connection (n300) run at exactly quarter speed, instead of about half, which I am getting with Archer C7 for example.

On archer, I got iperf on 20MHz channel about ~72Mbit/s, on 40MHz ~150Mbit/s.
On the usb RT5572 module i got ~30Mbit/s 20MHz and 70Mbit/s - 40MHz

I know, that USB wifi was not bright idea for router, just want to ask, if this is "normal" behaviour, or if there is something, I can do about it (some tuning?).
I was looking into change USB polling rate, but only solutions I found was for USB mices.

Is this the link speed and not a speed test? (Phy Rate)