If a general manager couldn't see Dalbec's long swing, inability to lay off the high fastball, low contact rates, and conclude that Dalbec was a risky player going forward, a player with a fringy hit tool, then that GM shouldn't be running a team.
Should Bloom have seen this? Yeah, why not. Fans saw it, you would expect a GM to see it too.
And Casas was probably a year away. Bloom went into this season without a competent plan at 1b, together with his horrendous OF decisions, and the fact that the Red Sox basically got nothing for Mookie Betts (Bloom's fault). All of these factors matter when evaluating Bloom--he has made a lot moves that didn't work out. He inherited a core of some really good players, Devers, Bogaerts, and Martinez has declined but can still hit. And Bloom completely failed to obtain some moderately decent offensive players to supplement that core. That's pathetic.