So is this a good reason to not join GBs and only opt for in-stock only?
Is it a good reason to completely avoid GBs? I don't think so.
Lots of great keyboards have and will be sold through group buys and I don't think you should avoid designs you love just because you can't immediately have it. I think you should look for GBs that are running with reputable vendors and/or designers who have fulfilled multiple projects successfully in the past. I don't think it's fair to judge the whole GB format based on this one GB that went wrong because of the runner's incompetence.
While an in-stock drop is obviously safer in that the seller already has the units made and (hopefully) quality controlled, GBs can't be avoided for bigger runner-fulfilled projects like this one. Getting the keyboards and all the necessary parts made is a huge investment that most hobbyist runners aren't able to fund upfront. This is why when you see an in-stock board with more than 10-30 units it's sold by a vendor most, if not all of the time.
Not to say that in-stock boards don't come with their own issues. Remember the F2?