Very low wireless speed on RB941-2nd stock firmware

Hello. I have very low wireless speed on my RB941-2nd. On RouterOS all my devices - two phones and a laptop are getting speeds about 5-10Mb/s. I’ve flashed OpenWrt and speeds have been increased to 40-50Mb/s on a phones and about 70-80Mb/s on a laptop. When i’ve flashed RouterOS back - there are still very low speeds. Tried different versions of RouterOS with no result. Also, i’ve tried different wireless channels, no matter, occupied are they or not, speeds are still the same. Is that something wrong with settings, or maybe it’s a bug in firmware?

Here are my settings for wireless interface:
name=“wlan1” mtu=1500 l2mtu=1600 mac-address=6C:3B:6B:5A:4F:F5 arp=enabled
interface-type=Atheros AR9300 mode=ap-bridge
frequency=2452 band=2ghz-onlyn channel-width=20/40mhz-Ce
scan-list=default wireless-protocol=802.11 vlan-mode=no-tag vlan-id=1
wds-mode=disabled wds-default-bridge=none wds-ignore-ssid=no
bridge-mode=disabled default-authentication=yes default-forwarding=yes
default-ap-tx-limit=0 default-client-tx-limit=0 hide-ssid=no


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Hey!
I have a quick question - where did you get openWRT for the mikrotik RB941-2nd?
I have been looking for this for the past while, it would really help if you post a link to the instructions or something.
Thanks for your time.

https://forum.openwrt.org/viewtopic.php?pid=349714#p349714

newer kernel(including updated drivers, btw0, toolchain, etc - do make difference, sometimes.