I've had the Reserve for a number of years, but had downgraded it to the DL Platinum last year. The main reason for holding either the DL Platinum or DL Reserve were the MQM boosts and MQD spend waiver as "insurance" for years when my business travels necessitated flying other airlines in any meaningful amount.
I do also value the 15% off points redemptions. Haven't been able to use the companion tickets in the past, but a more flexible schedule now will allow me more flexibility in planning leisure travel so that could become a useful benefit for me.
The new program changes make either card less necessary, as I have access to the SkyClubs via my vanilla AmEx Platinum. And I don't need the MQD boosts since the changes to the MM program now give me annual Platinum status. So I was planning to downgrade to the DL Gold card when my DL Platinum card comes up for renewal in September.

But I'm tempted by a recent offer to upgrade back to the Reserve - 50k Skymiles for $5,000 spend. And the addtl fee would be pro-rated from the fee already paid for the Dl Plat card renewal so only around $300. Really don't need the miles and the tie-breaker element for this card is no longer a major reason to hold the Reserve card. But it's amusing to observe my interest in taking them up on this - the habit of jumping at any opportunity to gain additional miles for card spend is hard to break!