Your iw list output confirms that while this router/build supports 2 streams...
...beamforming is not supported.
If beamforming was supported you would see output similar to this.
VHT Capabilities (0x339b79b2):
Max MPDU length: 11454
Supported Channel Width: neither 160 nor 80+80
RX LDPC
short GI (80 MHz)
TX STBC
->
SU Beamformer
SU Beamformee
MU Beamformer
MU Beamformee
<-
RX antenna pattern consistency
TX antenna pattern consistency