Was this one of the Boston Bruins worst trades in franchise history?

The Bs traded Jean Pronovost to the Pittsburgh Penguins on May 21st, 1968. He was traded to the Penguins along with John Arbour from the Bruins for the Penguins' 1969 first-round draft pick, who would end up being Frank Spring with the fourth overall pick and cash.

Pronovost was a consistent scorer who scored 40 goals four times. He was also the first member of the Penguins to score 100 points and 50 goals in a season. He would collect 316 goals and 287 assists in 753 games with Pittsburgh. John Arbour would only collect two assists in 17 games with the Penguins.

Frank Spring would only play one game with the Boston Bruins recording no points before being shipped to the AHL. He would go on to play for the St. Louis Blues and the California Golden Seals and collect 14 goals and 20 assists in 61 career NHL games.

The Bruins were fine as they would win two Stanley Cups in the 70s, but could they have won more had they kept Jean Pronovost?