My anecdotal business travel agrees with this assessment and it's not just D1 it also extends to PS and in some instances Y.

My company will pay for PS for international and DL has consistently been coming in with pricing that puts it at the same cost as J on UA and much more expensive than the PE on UA that my company will pay for (and no we don't have specific corporate pricing for UA that can explain this discrepancy). So instead I've been flying UA in PP internationally and had a pretty good hit rate of getting MUAs to clear to get Polaris in one or both directions.

I'm going to to stay PM on Delta again this year but solely due to the large rollover I started with, this non-competitive pricing has pushed the MQDs and MQMs I would need to organically get PM over to UA (where I'm pushing to at least maintain Gold after getting a Platinum match last year so I can keep E+ and *G benefits for next year)