For the watchonly wallet, we import addr() descriptors to bitcoind since it does not handle Miniscript yet. A descriptor must have a checksum to be imported to bitcoind. Back when i implemented this rust-miniscript did not have support for descriptor checksums. I used the hack of calling getdescriptorinfo before importing a descriptor to gather the checksum for each and every descriptor we import (hundreds on first startup).
Now that rust-miniscript does support them it's an unnecessary hack and performance hit. Replace it with just using the checksums provided by rust-miniscript.