Looks like we mac users just need to wait for the fixed software. This is the reply I got from LaserSoft Imaging:
the framework set we have for internal testing at the moment still shows the issue with
the different exposure value for 7200dpi. We have no installable test version of this at the moment. (…)
The final version that resolves the issue for 7200dpi is – as far as I know – still in development
on Plustek’s side.
Update December 19th:
So I asked to confirm whether they can confirm whether 3600dpi resolution scanning has the same issue. I got a swift reply:
the current driver version shows the different scan speed and the difference in brightness also for 3600dpi scans. We have a driver that works correctly up to 3600dpi, but sometimes shows the issue for 7200dpi.
I asked could I have that driver so I could at least scan with 3600dpi, the answer was no. So I asked when will the fixed software become available and got this reply.
I assume, that we will include it in the next update, or the update after the next one. This may be within the next 3 or 5 weeks.
I would certainly like if this would be included in the next update.
Therefore it seems that at present, mac users have no access to the higher resolutions.