I think the shaft provides a much better flux path for the magnets than the air gap between the claws... effectively short circuiting the flux from claw to claw, rather than jumping the air-gap.

With the original electromagnet, the shaft "became" the magnet and the return path for the flux was across the air-gaps. The shaft in your configuration now becomes the return path instead.

Solving this problem (with a magnetically inert shaft)will increase the flux density between the claws air-gap making it  the only decent flux return path.... increasing its effectivness markedly..... new shaft looks the ticket.

good use of old alts and microwave oven Joe.