For 10k passwords and 100ms per hash it is 90 hours of single threaded execution time.
There is no excuse not to do it, especially you need to do it only once per user (until password change).
There is no excuse not to do it, especially you need to do it only once per user (until password change).
That's 90 hours per account, multiply that by 326 million accounts and it's over a billion CPU days.
You can reduce it a lot (no need to spend time calculating the password for users who log in regularly, just wait for them to give it to you) but it's still a massive scale. Especially since the biggest risk comes from the millions of rarely used accounts.