BTW - Delta did offer to rebook me, but my family would have been split up. No-go with young children.

Since there are no seats on other flights, there's nothing that "courtesy" will do here. The "new" plane was pulled back from retirement. A340-600 should be in the desert, not transatlantic.
Delta: First-line agents have been outstanding - exemplary - the past year. Rebooking / waiving all fees, etc. Second-line agents (supervisors) are the office of "no", who was engaged here.
Virgin: Not helpful.

In summary, based on my last three trips on Virgin, I've completely soured on them. Brand-new 787-9 had buttons falling off the remote, seats were broken, and service was mediocre.
Delta has been far better - it shows Delta metal (hard product) has surpassed Richard Branson's propaganda from 30 years ago.