I mean it depends on how many people are working on it at once and how many people are reporting bugs I guess, but it just feels like Apple releases a new OS every week. You can't get great quality at super speed, it just doesn't happen. There needs to be a balance. If it ends up being a great OS then great, but I think it's not likely due to how fast things seem to be moving. What do I know though?
I will say that some of the features announced in Mojave excite me far more than the last few releases. They are finally adding some interesting things, rather than somewhat meaningless features. Like the new metadata view and the dark mode.