… that depends a lot of who you ask.
At the resolution of your test image, you should start seeing the film grain, especially in darker areas of the frame. If you really love to see film grain, go to a higher resolution. If you have a low-bandwidth internet connection (like I have), you will probably try to get rid of the film grain in the post anyway, in order to reduce file sizes. A higher scan resolution might help you with the reproduction of very fine details in your film - provided the camera used during the film recording is of sufficient quality (the one I could afford in the 70s of the last century was not) and the film stock is good enough (Kodakchrome, no Agfa, for example).
You seem to have a different problem. I have enlarged a cut out of your image:
Notice that the horizontal borders of all the resolution bars come out just fine, but the vertical borders show a zigzag-pattern? That is certainly no jpg-artifact. Probably has something to do with the read-out of the camera, treating even and odd lines differently. The last time I have seen something like that was with analog video cameras and framegrabbers not syncing correctly on the video signal. But this is a digital camera …