Nu and PDD are generating stronger growth at lower valuations.BigBear.ai (BBAI -2.41%), a developer of artificial intelligence (AI)-oriented analytics tools, has taken its investors on a wild ride since it went public by merging with a special purpose acquisition company (SPAC) three years ago. The combined company's stock opened at $9.84, rose to a record high of $12.69 in April 2022, but sank below $1 by December 2022.Like many SPAC-backed start-ups, BigBear.ai overpromised and underdelivered. It original ...