I fully understand your position. Even when "properly" optimised (according to my own definition of allowing people to play actively without an inherent penalty) there will be instances where holding off are optimal - and on the verge of a highly profitable tier would be one of those instances.
In terms of the opportunity cost of gold, I believe you do me a disservice. I admit I haven't crunched the numbers (because they aren't personally relevant), but having run through the event on normal I see nothing at all that would prevent a free player, properly dedicated, from completing the event (to the first stage). I'm quite sure that the gold efficiency of the second stage isn't up to normal gold efficiency of boss events - but given that syndicates are out that sholdn't be an issue. Syndicates are the best stats for gold option around, closely followed by building upgrade events (assuming one has in-game cash).
The larger issue is that so little action has occurred for so long that the idea that bosses are the only viable stat-booster has become doctrinal. It is my believe that due to recent events that supposition is no longer necessarily true.