This is an interesting predicament you’re in, however I think the answer is simpler than you think.
OpenWRT is no different than other distros like Debian or CentOS. They are all standard Linux. They all run the Linux kernel, some more updated than others. If you have issues with OpenWRT, you’ll experience the same issues on Debian.
You can run Debian on OpenWRT devices with enough hacking, but you will end up in a worse situation than you would be with OpenWRT, which is designed for embedded devices.
Your choice of distro could actually increase/decrease the lifespan of your device, too. If you chose Debian, which isnt designed for embedded systems, you may face an issue in the future where your NOR chip or NAND chip has begun to fail because Debian has no optimizations for NOR/NAND flash IO.
The main problem with distros that are not designed for the hardware you are running is packages. Packages must be compiled for your CPU architecture before they can run, which is why Debian’s standard repository will not work on GL-Inet devices. Most of GL-Inet devices and routers in general run MIPS, not X86/X86-64 which is what desktops run and what the Debian standard repository is compiled for.
If you wanted to run what is your definition of “standard linux”, you will spend way more time trying to maintain your own cross-compiled repository which could be hundreds of gigabytes, and your own fork of the distro designed to run on your hardware of choice with the required drivers.
You might want to look into LEDE, which GL-Inet devices can run without any problems.
OpenWRT and LEDE have the only standard repository’s that are cross compiled to almost every CPU architecture you can imagine, including MIPS.
LEDE is generally more updated and designed for general embedded systems and not just routers.
Regardless of what distro you choose, as long as you choose a stable version of it, you don’t need to update the devices very often.
If you must update the devices often, you might want to consider forking your own version of the stable version of the distro you choose and the repository too.
I don’t really know what you mean by “converting the devices too often”, but if you mean flashing them with OpenWRT, you only really need to flash them once.
Adding an auto-updater shouldn’t be hard either, which can be used to automatically update thousands of devices at once without trying too hard to maintain them.
As mentioned in an above post, if something fails it is not very hard to recover the devices with the serial pins or the Uboot web interface on GL-Inet devices.
Uboot web interface is my preferred way to reflash firmware when I don’t have access to the firmware for whatever reason.
In any case, I believe that the solution to your problem is simply OpenWRT or LEDE. The firmware you create with OpenWRT and LEDE can be cross compiled for almost any architecture you can imagine. The only differences would be the drivers that the devices require. OpenWRT and LEDE can even run on X86/X86-64.
GL-Inet has device profiles in both LEDE and OpenWRT, so it is also very easy to create your own firmware for them by compiling it with the provided device profile. This will auto-select all of the necessary drivers to run on the target device.