The only thing this suggestion does is allow you to choose which defense you get. Assuming 2h vs shield+1h, it will not give you another defense, nor will it make you lose one.
No, spirit shield does not give you the shield block proficiency, it just gives you a virtual 0 AC shield that can't be disarmed and leaves your hand free. Just because you can wear a shield, doesn't mean you're going to block with it. This suggestion means that should the healer go the two-handed weapon route, they shouldn't bother practicing spirit shield.
If you choose two handed, with one command you'll lose both of your defenses when someone disarms your weapon. Where's your god now? Additionally, fewer classes have the ability to disarm, cleave or otherwise remove shields.
Yes, healers can craft a one-handed staff. That's pretty significant when combined with a shield. That shamans can use staffs means little in regards to this. There's only 3 standard classes that can't.
Every staff (with the exception of healer/druid staffs and the awl pike) is two handed, by the way.
I'm not certain where you think that wielding a two-handed weapon is often needed. Sometimes, sure. Often? No.
No, this isn't a rehash of the "2h block <> shield block" discussion from previous.