As I see it it all comes down to this:
Having a tier system is a good idea, but he existing classification mechanism is flawed. It's flawed because regularly killing it in tough conditions is ultimately no different than eking out a 29 or 30 once in a while from short tees to slow greens in low wind.
The best way to fix this is to make it a two-way street. Demotion has to be a possibility. Membership in any tier must be both earned and maintained.
A player could be classified based on a true average over the previous X number of rounds OR credits earned (and by earned, I mean after the initial wager is returned) in all formats including RGs, brackets, MP, skins and blitz.
Earnings could be displayed as a rate stat, too: +112 credits per 18 holes, for example. Or -17 or -56 or +21. That might be a better way to express it. It could be calculated over all rounds or just for rounds with money at stake.
There's a simple answer for sandbagging, which is that a player cannot move down until more credits have been lost than were earned when moving up. For players who don't gamble, only the scoring average needs to be used.
Promotions would occur immediately, demotions would happen at the end of each month. Averages for each tier wouldn't be fixed, but could change as the game evolves.
There are already enough tiers. If each of the existing eight tiers includes a four stroke difference in average, that's 32 strokes among them, or averages ranging from 55 to 87. Want tighter groups? Three strokes still gets you from 55 to 79. Anybody with an 80+ average doesn't need their own tier, they need to practice.
I'm sorry if this is long and messy. I wound up just throwing some ideas out there. Point is, I think the best thing WGT could possibly do is to junk the current system and start over. Short of that, at least try something different (like the Q school and tour) for any new tier. X average over best Y rounds doesn't work.