For existing card holders, The Platinum Delta SkyMiles Amex does not appear to offer me (as a Diamond Medallion) any significant benefit over another card. Please help confirm my reasoning based on the following:

1. I don't need to collect more Delta miles, would prefer cash-back. So bonus/multipliers are not of value to me.
2. As as a DM, I plan to earn enough EQMs and EQD's next year that spending on the AmEx card to waive the limit may be redundant.
3. I don't have interest in a companion certificate, I have enough miles I can buy companion tix with those.
4. I already get Sky Club access as a DM

For $150/yr, what does this card really give me? Is there something I am missing? Seems like I should cancel before the annual fee hits. Amirite-or-what?

Thanks!