"I'm trying to think of a case where there wasn't a pretty ordinary explanation for the differences in outcome. Perhaps you could point me to one?"

Sure. DOJ decisions:

The decision to not have charged Hillary or Huma for classified material but to charge trump but not Biden.
The decision to raid Mar Lago but not Bidens garage
The decision to allow the statute of limitations run out on Hunters tax charge
The decision to all Hunters tax evasion to not be prosecuted (so much for everyone paying their fair share)
The decision to attempt to get a sweetheart slap on the wrist deal while others have gone to jail for the degree of Hunters
tax evasion
The attempt to get a pardon for Hunter for all past as well as any future crimes he may commit.

Two tiered justice writ large.