VS isn't big enough to get economies of scale in widebodies as it is. Fourteen 330s (maybe declining), seventeen 789s and ~eight 339s is pathological. Then add some A350s to that. They could be an all-787 fleet. They might get some economies of service and parts from Delta's 330 and 339 ownership but it's hard to say how much.
A mixed A332/333/346/351/747/789 fleet does seem diverse for an airline operating 44 aircraft. By 2022 that will slim down to 332/333/351/789. Many airlines (BA included) are planning to operate a mixed A350/787 fleet, of similar sizes to VS. The difference is that they have large narrow body fleets, but there is limited benefits of scale there.
As I remember the A333s were to cover the 787 delays and the 4 A332s were an opportunistic grab when Air Berlin went under. I think the A330s also had the benefit of using up the A380 deposits, but I can't 100% remember that, so they are likely to be weighing up their options. Send the A330s back, as per the original plan (but replace them with 330neo, rather than 787s) or to extend the lease on them.
For the lower demand US routes the A330neo seems a reasonable choice. I'm sure they could use the 789 on these routes, like BA does, but It depends how sharp Airbus' pencil is. How keen are they to get more A330neos out the door?
Anyone can under sell anything, depending on the depth of their pockets.
Boeing had an objective, and it wasn't profit, but to curtail A330NEO sales in the USA.
Doubt the sale package broke even, after waiving early termination penalties and EOL payments on the 767's.
A bit like the UA 737-700 order against the C-Series, I guess. On a per-unit basis it might not make much sense, but strategically the decision looks different. In the end that strategy probably hasn't worked in Boeings favour, but the idea was there.