All people are miffed about is that the production values slip sometimes, and compared to the part 1 anime this isn't much. They need to take a break between cours like they did with Stardust Crusaders.
To address each of your points in turn:
1. "Production values slip sometimes"
This seems to be an overly generous assessment of the situation.
I would argue that the frequency of the "production value slips"
have been increasing over time until they make up a larger and larger percentage of each individual episode.
The last few weeks have been steadily declining in terms of their ration of acceptable art vs bad art until we arrived at last weeks episode where +50% of the episode looked awful.
2. "and compared to the part 1 anime this isn't much"
You can't set the bar that low and then congratulate the show for clearing it. Yes, compared to
Mars of Destruction,
DIU is a far better produced work. But on any other scale it's comes out less favourably.
A far more useful comparison isn't
JoJo's Part 1 but the start of
JoJo's Part 4 where the series looked good every single week.
Finally, your argument makes the assumption that the
only thing people are complaining about is the production values e.g. the spotty art. But what I, and others, have complained about is the declining quality of the direction. The earlier parts of this adaptation were noted for their strikingly creative transitions and generally slick direction, These powerful directorial flourishes have all but disappeared as the show entered production crunch. This is as a big a problem, if not a bigger problem, than inconsistent art.