Though comming from very early gl-inet routers.
As consumer what pokes my interest is that it comes with a easy ui and OpenWrt.
I know with the era of Flint 1, we were stuck for a extremely long time on OpenWrt 15.5 and basicly I would have thought GL-iNet never again would make these mistakes.
Though wether you like it or not, here we are again.
I learned that it is either because of the lack of stable wireless they rather choose vendor sdks which in long term work more imutable/reliable thats the reason the OpenWrt base is so ancient because it always works, but as I know this is not comparable at all but a mindset, personally I think GL-iNet needs to listen very carefully to this demand, personally its the damage control making them stuck, and personally when I look to the whole Flint 2 situation and the sticky on the download page about the op24 firmware, I see no reason why not to do it... It works very good aslong you keep it on the releases maybe now minus one candidate less because of the APK introduction and wifi-scripts-ucode these deff could pose breakage.
What I get however from the message is a false sense that OpenWrt is bad, it isn't true.
But it is also what is on supply and demand with the chips, and this made them to go with qsdk in more recent routers.
I hope the company learns about their true OpenWrt fans 
Back then it had nothing to do with enterprise level styled routers, it's a total different audience but more of the hobbyist where mistakes where allowed.
I really want to have this low level a bit back, i read some comments here, it doesn't match what this company standed for when I joined this forum , it was always open for things and now I read people need to buy a other router if they disagreed, crazy.
Sure all routers even non branded ones use old OpenWrt bases in their propetairy MTK/QSDK forks, but I bought them purely for OpenWrt with the ui.
Great example:
My first router was the MangoV2, I think that was the way to go, as far as I know it always used recent OpenWrts.
Before I invested in possible the worst routers you can imagine as target for OpenWrt like a bunch of old tp-links 1043nds, and linksys they always had quircks with wifi due to OpenWrts issues with Qualcomm, GL-iNet routers where the first full complete packages which didn't had those issues.
The Flint 2 also proofs this, I have also had some other routers to test like the ax6s but there were still some issues with OpenWrt or that partition layouts got changed it are never fun things, for me this often invites me to cold brick my device because I hate reading the documentation for this change hence the warnings on the sysupgrade page 
If they just step back at:
OpenWrt + nice gui
And then keep OpenWrt recent aslong these possibilities are there, I see no issue, I agree with OP with most of the things.
But it is important to know such ancient kernel doesn't necessary mean you are vulnerable in security GL-iNet can also choose to backport things, I rather trust them than a tp-link firmware