anyone know what dooku just didn't commission elite magna guards to capture the chancellor instead? surely he could ask the holotech engineers to create some?
Same reason Vader didn't use them in TESB? Maybe it's cheaper to hire a few expendable bounty hunters than to invest the resources that would be required to create highly sophisticated pieces of droid technology. (The rank-and-file combat droids are presumably so stupid and inept because they're simple enough to be mass-produced.)
Or maybe it's just because
Star Wars is a fantasy and has never really made any pretense of being plausible. Dooku's using bounty hunters because bounty hunters are an established conceit of the SW universe and the writers wanted to do a story about them.