The A7 v5 is a rebadged C7 v5 which has a weak single core Atheros MIPS SoC.
Performance of opens source firmwares are unlikely to match stock firmware for maximum throughput. This is mostly due to limitations of open source drivers provided for 'free' by the chip manufacturers.
Use Openwrt because you want access to features which are not available with stock firmwares.
If you want to improve wifi performance, install a wireless access point running OEM firmware, wired to your OpenWrt router.
https://forum.openwrt.org/t/archer-c7-v5-poor-wireless-performance/53854
https://forum.openwrt.org/t/solved-openwrt-performance-on-tp-link-ac1750-archer-c7/23239/3