Let's take a step back.
6,2M openwrt-23.05.2-ath79-generic-tplink_archer-a7-v5-squashfs-sysupgrade.bin
On an 8-MB-flash devices that leaves you with around 1.5 MB free space after flashing, not deadly, but not great for comfort either - and certainly not much space left for installing additional packages.
Expect that to grow by around 100-200 KB per LTS kernel release on average, some more churn on userspace and potential changes to the package line-up (e.g. WPA3 support required adding a ssl/tls provider, going from wolfssl to mbedtls saved a little space again, …).
Obviously you can fill that up quickly with large packages (samba is an obvious candidate for this) or multiple more sensible packages, but OpenVPN isn't that much of an offender here by itself (obviously wireguard would be smaller).
Semi-related, I tried to build a minimal OpenWrt/main for a tl-wr941nd v2 over the weekend, no opkg, no PPPoE, no luci, no flow-offloading, only wpad-mini (no WPA3 support).
kernel v5.15:
[ -f /tmp/pkg/openwrt/build_dir/target-mips_24kc_musl/linux-ath79_tiny/tplink_tl-wr941-v2-kernel.bin -a -f /tmp/pkg/openwrt/build_dir/target-mips_24kc_musl/linux-ath79_tiny/root.squashfs+pkg=e9fb4539 ]
/tmp/pkg/openwrt/staging_dir/host/bin/mktplinkfw -H 0x09410002 -W 2 -F 4M -N "OpenWrt" -V r25029-07ea729761 -m 1 -k /tmp/pkg/openwrt/build_dir/target-mips_24kc_musl/linux-ath79_tiny/tplink_tl-wr941-v2-kernel.bin -r /tmp/pkg/openwrt/build_dir/target-mips_24kc_musl/linux-ath79_tiny/root.squashfs+pkg=e9fb4539 -o /tmp/pkg/openwrt/build_dir/target-mips_24kc_musl/linux-ath79_tiny/tmp/openwrt-ath79-tiny-tplink_tl-wr941-v2-squashfs-sysupgrade.bin.new -j -X 0x40000 -a 0x4 -s && mv /tmp/pkg/openwrt/build_dir/target-mips_24kc_musl/linux-ath79_tiny/tmp/openwrt-ath79-tiny-tplink_tl-wr941-v2-squashfs-sysupgrade.bin.new /tmp/pkg/openwrt/build_dir/target-mips_24kc_musl/linux-ath79_tiny/tmp/openwrt-ath79-tiny-tplink_tl-wr941-v2-squashfs-sysupgrade.bin || rm -f /tmp/pkg/openwrt/build_dir/target-mips_24kc_musl/linux-ath79_tiny/tmp/openwrt-ath79-tiny-tplink_tl-wr941-v2-squashfs-sysupgrade.bin
[mktplinkfw] rootfs offset aligned to 0x1748116
[mktplinkfw] *** error: images are too big by 696980 bytes
kernel v6.1:
[ -f /tmp/pkg/openwrt/build_dir/target-mips_24kc_musl/linux-ath79_tiny/tplink_tl-wr941-v2-kernel.bin -a -f /tmp/pkg/openwrt/build_dir/target-mips_24kc_musl/linux-ath79_tiny/root.squashfs+pkg=e9fb4539 ]
/tmp/pkg/openwrt/staging_dir/host/bin/mktplinkfw -H 0x09410002 -W 2 -F 4M -N "OpenWrt" -V r25029-07ea729761 -m 1 -k /tmp/pkg/openwrt/build_dir/target-mips_24kc_musl/linux-ath79_tiny/tplink_tl-wr941-v2-kernel.bin -r /tmp/pkg/openwrt/build_dir/target-mips_24kc_musl/linux-ath79_tiny/root.squashfs+pkg=e9fb4539 -o /tmp/pkg/openwrt/build_dir/target-mips_24kc_musl/linux-ath79_tiny/tmp/openwrt-ath79-tiny-tplink_tl-wr941-v2-squashfs-sysupgrade.bin.new -j -X 0x40000 -a 0x4 -s && mv /tmp/pkg/openwrt/build_dir/target-mips_24kc_musl/linux-ath79_tiny/tmp/openwrt-ath79-tiny-tplink_tl-wr941-v2-squashfs-sysupgrade.bin.new /tmp/pkg/openwrt/build_dir/target-mips_24kc_musl/linux-ath79_tiny/tmp/openwrt-ath79-tiny-tplink_tl-wr941-v2-squashfs-sysupgrade.bin || rm -f /tmp/pkg/openwrt/build_dir/target-mips_24kc_musl/linux-ath79_tiny/tmp/openwrt-ath79-tiny-tplink_tl-wr941-v2-squashfs-sysupgrade.bin
[mktplinkfw] rootfs offset aligned to 0x1832496
[mktplinkfw] *** error: images are too big by 789223 bytes
That was the moment when I took my four remaining 4/16, 4/32 devices (wrt-54gl, wl-500gx, wl-500gPv1, tl-wr941ndv2) from the shelf and put them into the recycling bin. Could I recover a little more space with even more agressive stripping (who needs printk's (right?!), wireless, a firewall, an sshd; using more agressive squashfs parameters at the cost of RAM usage (of which there isn't much to spare, 32 MB)), sure - would that free up 800 KB, no (and to be frank, neither of them had been in production use for almost 15 years - nor gotten out of the shelf for more than 15 minutes at a time in a decade; last touched/ powered-up/ flashed in mid 2018).