Hi,
I'm not aware of a good way except of these two interfaces (perhaps also the same command via ZAPI/new ONTAP API).
The other things I would have try are:
1. to robocopy the folder-structure-only into a VM and try to run it locally (to avoid network latencies on the queries)
2. be sure to have small latency to AD and enough processing capacity on it as well
3. use filters on the get-acl to only include non-inherited permissions - so again you'll fewer queries to AD.
4. try to use another method to query the SMB. Maybe also try without translating the SIDs and doing it later based on your own index https://www.reddit.com/r/PowerShell/comments/69181h/getacl_is_looking_up_sids/
There's of-course commercial tools that generate folders audit and allow you to act on it. you can consider using their tools instead of developing your own. I also mentioned it as for my experience, Varonis for example do their scan via SMB, and it can take a day or two for a 10TB share to get scanned (on an AFF).