With Delta at selling 88% of First Class upfront, the value of Diamond Medallion upgrade priority is dropping to near-zero. Assume a moderate frequent flyer profile:

• Volume: 20 trips/year at $500.
• Delta Premium: Delta commands a ~20% price premium over UA/AA/AS.
• Cost of Loyalty: On $10k spend, you are paying a $2,000 premium just to fly DL.
• To break even on that $2,000 loyalty tax, you need a return. If you value a cleared upgrade at ~$400, you need 5-10 upgrades per year (a ~25% success rate) to justify the extra cash.

At an 88% paid load factor, achieving 25% is mathematically impossible on most hub routes. There just isn't enough inventory left for the gate lottery. Obviously, this may vary significantly by route. But if you audit your routes and F is consistently >80% sold 48 hrs before the flight, you are paying a premium for a benefit that doesn't exist. In that scenario, you're better off taking that $2,000 annual savings and just booking confirmed F on a competitor.