With public market valuations of B2B companies today, I could see Plaid being worth considerably more than the $5 billion that Visa agreed to. I think it's less likely buyer's remorse than just overwhelming evidence of anticompetitive behavior. The original DOJ complaint [1] has a lot of direct quotes from top level Visa execs. See paragraphs 9 and 10.

[1] https://www.justice.gov/opa/press-release/file/1334726/downl...