I get where Cory's coming from, but didn't God of War have massive leaks? Down to even art design documents hitting the internet. I don't think that took away from the reveal. Hell, they even had a whole bit in their documentary on the reveal of God of War; one of the most hypest/exciting moments at an Sony press event that was leaked in earnest.
But on the flip side, take for instance Mario + Rabbids: after the leak of marketing notes before E3, I don't think anyone was excited for that game until they showed it off. Those leaks definitely hurt the game heading into E3. It had an uphill battle and in my opinion succeeded after the stage presentation at Ubisoft. I don't know if other titles could have pulled that off.
The common thread is that both titles were well constructed games that had a great initial, in-depth showing/demo. And I'd argue that's what's really important.
Leaks be damned, people are probably gonna buy if you show off a good game. You don't even need to show off a good game! Even a manipulative polished up vertical slice demo like Anthem had people buy in, but that's another issue besides leaks.
Withholding the existence of a product is marketing, sure. Do it for the surprise, but you gotta admit shit is low stakes if you feed off a hype machine. But it's their job to sell it so I guess they got the job done?
I do admit, you gotta feel a little bummed to keep a secret for so long only for it go public days before you do it yourself. Hazards of a giant, unchecked industry going into a public event I guess.