You're under the same obligation as top and jungle to pick what suits the team. And, unfortunately, those top and junglers are thinking the same thing. That you and the other role capable of picking tankier options should do it instead of them. If all three of you can't communicate enough to get even one initiator champion then you're all just plain bad and you can't pin it on top/jg exclusively.
I'll agree with you on the items thing, I've had SS-less supports do more work and ward more than ones I've had with SS. If you're getting the job done then you can do it how you want.
They don't own you but they still rely on you. If you don't give them warning about when you're roaming, you're very much at fault for them being 2v1'd. When you show your face mid they will go for your ADC, even under tower if they're able. And if you haven't communicated to your ADC that you are leaving...you're a bad support. :\ That's just how that is.