The standard benefit of the DL Plat Amex is a 10k MQM + 10k RDM "MilesBoost" once you spend $25k in a calendar year on the card. You get a second 10k MQM + 10k RDM if you spend another $25k that same year (total $50k spend). Max of two MilesBoosts per year.

The offer you got for 5k MQM + 5k RDM to upgrade from Gold to Platinum is the standard one available once you've had your Gold card for 13+ months. As others have said, you'll likely get a better offer by signing up for a biz version of the DL Plat Amex, or by cancelling your personal DL Gold Amex now, and then applying for a new personal DL Plat Amex in 90+ days.