I'm probably among the lowest possible Diamonds out there under the current rules. I have an MQD exemption via a foreign address (and as such, I can't view my MQDs on the app, but I would estimate it to be ~$6000 pa with ~$3000 spend on actual Delta flights). I have an AMEX card but I hardly ever use it for non-flight purchases because it is of limited use where I live. I fly low CPM long haul routes, and probably half of those itineraries I bargain hunt. And I travel significant portions on VOZ which isn't even a part of SkyTeam.
With that being said, I can only think of one occurrence where I feel like I was kind of getting the short-end of the stick and was disappointed Delta didn't do more for me in the rule-bending department. Long story short, I was going to spend about ~$1,200 on a MEL-LAX flight but needed to reschedule an LAX-ORD flight that was on a separate itinerary. There was a schedule change but it wasn't "enough" of a schedule change, despite getting an email saying that I *may* be able to change my itinerary. I was meeting someone in ORD so didn't really want to risk a long day of stand-by. I HUCB once but eventually just decided to bite the bullet. I think I ate it to the tune of about $600 or so.
Besides that, I am regularly upgraded, never observed any weirdness going on with my upgrade placement. I have GUCed LAX-SYD 1/2 times so far. And overall I feel as though I am treated like any other Diamond. I certainly will enjoy it while it lasts, as who knows how long the MQD exemption will exist for foreign address holders.