Steering effort for manual 16:1 - should it be this high?

The amount of positive caster is helping to make the situation worse, but, it's not going to make a huge difference reducing it. Maybe if you went down to 2* but then, you're right back in stock crappy caster territory. I'm not sure you'd see an appreciable difference lowering it to 3*........you might, but it's not going to be night and day. I didn't see what car this is, but if it's the late A body in your avatar, that doesn't help either, as they are a good bit heavier than the early cars.