Is slow on purpose a good idea? Pabbly thinks so.
Most email list verification services brag about how fast they are, and when you're trying to validate a list of 100,000 email addresses, or just 1,000, speed does help. And in our experience, you can be accurate and still be quite fast, by employing some tricks of the trade that can kind of lump certain verifications together, and you can run multiple verifications in parallel to save time.
So does it make sense to be slow on purpose? Maybe. If you properly manage your time, you should have plenty of time between when you verify and when you need to run campaigns, as long as you don't put everything off until the last minute.
And since companies can do email verifications both accurately and quickly, it's a bit of a weird flex.