The LoRaWAN spec
It is, to say the least, complicated with a lot of things that are fairly hard to implement in practice… most implementations have had a long path to sound functionality, with or without spec compliance. That said, rather than an argument for handing over the task, I personally see this is a reason why it is absolutely critical that the code lives where one can fix it.
To address the original question, I think there’s a thread around here somewhere about the Heltec PSoC + SX1262 offering but do not remember the details. And I think I might(?) have seen some hints in the pycom microphython node side implementation (while looking for the gateway code they seem not to have published). LMiC does not seem to have it as it would be substantial work to switch radio interfaces. One could check if the more official LoRaMACNode stack has support… rereading I realize that list is heavily biased towards codebases that hopefully work but are maintainble rather than canned solutions with “no user serviceable parts inside” as the asker was apparently seeking.
Ultimately, the best all-around solution may be something that is believed to work in the condition in which it is sold, but where the code that makes it work is in a public repo, and where someone independent of the manufacturer reports that they’ve successfully built and flashed that. Seeing a 3rd party pull request for some small fix would thus be an encouraging sign.