Drilling a hole in the drive enclosure which passes through all the platters will make it impossible to run the drive. Most modern HDDs don’t have air inside the enclosure, and you’ve let what was in there escape. You’ve filled the cavity with tiny pieces of drill swarf, which will be on everything including the platters, and will crash the heads if someone tries to lower them onto the rotating platters. You’ve also unbalanced the platters, though I don’t have an estimate for whether this will be fatal. The drill bit will likely pass through the controller board on the way, which though not fatal will certainly not help anyone trying to hook the drive up.
You have not prevented someone from putting the platter under a magnetic force microscope and reading most of the data off that way. We can be fairly sure this is possible, because the SANS paper linked from the linked SF article demonstrates that you can’t recover data from a platter with an MFM after a single overwriting pass, and such a test would be completely meaningless if you couldn’t recover non-overwritten data using the same procedure.
So drilling through the platters will very likely prevent data from being read off the HDD by normal means. It won’t prevent much of the data being recoverable by a determined, well-funded opponent.
All security is meaningless without a threat model. So decide what you’re securing against. If you’re worried about someone hooking up your old company HDDs and reading them, after they found them on ebay / the local rubbish dump / the WEEE recycling bin, then drilling is good. Against state-level actors, drilling is probably insufficient. If it helps, I drill most of my old drives, too, because I am worried about casual data leakage, but I doubt the security services are interested in most of my data. For the few drives I have which hold data that Simply Must Not Leak, I encrypt them using passphrases of known strength, and drill them at the end of their lives.