I gather that the serial was a pretty literal adaptation of the radio series, perhaps even a direct remake of some of its episodes. And a weekly series could drag out things like that a lot longer and have Casey get involved in the stories a lot more intermittently or gradually.
But if so, then yes, it was a weakness, and it goes to show how unwise it is to adapt something too literally, since what works in one format or medium may not work in another. Casey's small role here was a disappointment and a waste of an interesting actress.
But the actress, Anne Nagel, did return in the second serial, so maybe she had more to do there. It also brought back the same actors as Axford and Kato, though Britt was recast (as was the Hornet's voice) and Jenks was replaced by a different reporter. (And the bad guy was the same actor who played Perry White in the Superman serials!)