Earlier quoted context omitted.
If they are doing this to 125,000 accounts, they should get an average of one account per day, right? So on average it would on average take them 342 years to get any specific account, but as long as they aren't trying for any particular account, they've got a pretty good ROI. I guess the fix for this would be exponential backoff on failed attempts instead of a static quota of 4 a day?
Why would doing this to 125K accounts give them access to one account per day? The chances of guessing 6-digtis pin code for each account is the same (10^6) regdless of how many accounts your are attacking
Imagine the extreme case, where they pinged one million accounts and then tried the same code (123456) for each one. Statistically, 1 of those 1,000,000 six-digit TOTP codes will probably be 123456