This is a great question, and falls inside the general territory of ''When is a safe practice or safety gear unsafe...?''
Just a clarification, so we''re talking the same language. A preventer typically refers to a line
run forward from the boom end (or nearly so) to the foredeck somewhere, and then perhaps/perhaps not back to the cockpit. It''s purpose is to prevent an accidental jibe & the damage it may cause (such as your experience). A boom vang can run from the mid-boom area to the sidedeck (and maybe back to the cockpit), and is intended to flatten the mainsail on a reach/run. OR these days, can be an in-line vang of some kind, tacked to the mast base and would do ''zip'' re: a jibe. IOW it''s a trimming device, tho'' it may/may not serve partially as a preventer.
I''m guessing that you made your initial decision (not to hook up a preventer) based on your normal racing/sailing experiences, which I''m betting are on the Bay. Then you found yourself offshore in more swell & boat motion than your crew typically faces, and the sea contributed to the jibe. Or put in the form of a question, did you make your ''no preventer'' decision based on Bay racing but find yourself in seas that more typically would call for one?
Another question is whether you have a boom vang and/or boom brake on the boat? I''d expect at least the former on a racing boat, but if it''s an in-line vang (vs. taken to the side deck) that''s irrelevant to your question re: a preventer.
FWIW some form of preventer can be a good fundamental practice offshore, especially when short-handed - at least, when sailing conservatively. Racing is a different ballgame: more crew & more alert on-watch crew (arguably, good reasons not to bother with a preventer), racing closer to the jibe, keeping lots of sail area up & more boat motion (just asking for a jibe!). Sounds to me like a judgement call, and your experience is suggesting for those conditions & your crew, a preventer was the wiser choice.
My wife & I are doing frequent offshore sails right now, and I rig
a sidedeck boom vang and reef down conservatively to avoid having to deal with situations like the one you had to tackle. And at night, even more so! I know our circumstances don''t equate to offshore racing...but perhaps to some degree, they should. Thankfully, we didn''t hear you say anything about crew injuries...which would even more strongly suggest a preventer of some kind would have been a good idea.