@fakemanhk Thank you for your reply. Ah, a great point and that makes sense. It was my confusion on what Evenroute was doing, but instead of fully dissecting that (which I had a fun afternoon trying below), I 100% agree OpenWRT's defaults are the way to go.
@mk24 Thank you, as well, for your reply. I appreciate your confirmation; I'm sighing with relief here. For what it's worth, the name of the model 2006 is likely the Qotom Mini PC Q750G5 S08 (OEM link here).
@frollic Thank you, as well, for the great advice pointing me towards the simpler and better solution.
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Just for my edification, I was curious just which packages & dependencies are in our current Evenroute build. I split it into two categories (neither are 100% accurate; I often only went 2-3 levels deep to save my time):
These account for ~65% of the 270+ packages. The remaining 35% are things I don't expect to use, e.g., mDNS, VPNs, DDNS, ipset, mounting / storage, USB, development, automation, etc. It took a fair amount of Google'ing to figure out what the remaining packages do (and a lot of CTRL+F between NotePad++ windows, haha).
Thus, for me, the current packages (except dnsmasq) listed by the firmware selector for OpenWRT 23:
base-files busybox ca-bundle dropbear e2fsprogs firewall4 fstools grub2-bios-setup kmod-amazon-ena kmod-amd-xgbe kmod-bnx2 kmod-button-hotplug kmod-e1000 kmod-e1000e kmod-forcedeth kmod-fs-vfat kmod-igb kmod-igc kmod-ixgbe kmod-nft-offload kmod-r8169 kmod-tg3 libc libgcc libustream-mbedtls logd luci mkf2fs mtd netifd nftables odhcp6c odhcpd-ipv6only opkg partx-utils ppp ppp-mod-pppoe procd procd-seccomp procd-ujail uci uclient-fetch urandom-seed urngd
plus these custom packages (listed separately purely to make it cleaner on the forum, but will actually be combined above) for the features I use today:
dnsmasq-full stubby luci-app-sqm luci-app-upnp luci-mod-network luci-mod-system luci-mod-status htop
DNS caching & authoritative, DoT, SQM, UPnP, and the current LuCI interfaces we have now, in that order.
My final task is to compare the network monitoring / measuring packages (as Evenroute had a great feature in their pre-EOL builds that had human-readable timestamps of when the WAN connection went down and ran daily speed testsâsadly, all cloud-based). I can't promise I'll find something quite the same, but it's worth a try.
And to get quite familiar with the OpenWRT restore process, just in case. 
To my pleasant and grateful surprise, and anyone that used Evenroute's basic UI, stubby (DoT / DNS over TLS) can be configured in LuCI (the OpenWRT web GUI interface) as long as you're OK with Cloudflare as your only DNS provider.
Thank you sincerely to everyone in the OpenWRT community, especially those here in this thread. We couldn't have made it this far without your great efforts.
//
I will update soon (1-2 weeks) how the final install goes and maybe turn this post or a follow-up post into a step-by-step guide, for those of us Evenroute customers that might need a helping / close hand at starting from "scratch". I hope that is all right to share in this thread, even as for many OpenWRT veterans in this thread, it will seem really redundant (though OP, please let me know if you're tired of the notifications).
