I have been through with the power settings already. In fact, on a TL-WR1043ND v3, setting the region correctly (in my case BR) has the driver operate at 14 dBm. Using the driver's default (US), it can operate at 25 dBm, although that does not mean the hardware is capable of operating at such power.
This discrepancy seems to be caused by the ART EEPROM, as the regulatory db shows the same 2.4G rules for BR and US (other than the additional 12 and 13 channels).
country BR: DFS-FCC
(2400 - 2483.5 @ 40), (30)
country US: DFS-FCC
(2400 - 2472 @ 40), (30)
I also couldn't find anything on OpenWrt's ath9k patches that would reduce the power for BR, but not for US.
As for 5G, BR allows for up to 27 dBm in the lower frequencies, which is what I am using in order to increase wavelength.
country BR: DFS-FCC
(5150 - 5250 @ 80), (27), NO-OUTDOOR, AUTO-BW
country US: DFS-FCC
(5150 - 5250 @ 80), (23), AUTO-BW
This one works correctly and the driver is operating at 27 dBm, but as mentioned, this value could be much lower because of the hardware.
(2.4G disabled on this one, ath10k-firmware-qca9888 + kmod-ath10k-smallbuffers, no other 5G APs around)
config wifi-device 'radio0'
option type 'mac80211'
option path 'pci0000:00/0000:00:00.0'
option channel '36'
option band '5g'
option htmode 'VHT80'
option cell_density '0'
option country 'BR'
config wifi-iface 'default_radio0'
option device 'radio0'
option network 'lan'
option mode 'ap'
option ssid '...'
option encryption 'sae-mixed'
option key '...'