There is a bug in large meter size in condensed score.
It looks like Dorico applies the “four or more staves” large meter size to 2 condensed staves.
IOW, even though the condensed score shows only two staves, Dorico counts them as four.
I wouldn’t consider this a bug, though I would agree that it’s not always helpful behaviour. Dorico behaves the same way when it comes to staves that are hidden on a given system: to keep the size of the meter consistent from page to page for the same group of instruments, it uses the size for the uncondensed or unhidden staves in the family/bracket. Condensing can of course change from system to system, just like staves being hidden and reappearing, so we prioritise a consistent appearance. Other approaches would of course be possible for us to add in future versions.
Unless I misunderstood what you wrote, Dorico doesn’t count hidden staves while calculating the size of large time signatures. To me, this is the expected behavior. The alternative would be clashing time signatures in optimized scores (with hidden unused staves).
Ultimately, this comes down to a general design choice you described in another thread:
I kindly ask you to reconsider this approach, to include optimized scores as well.