>What this really does is remove the ICC's authority.

Not yet. The UK and Italy both declared that they would be legally obligated to abide by the decision, which is unprecendented and historic in itself. Sure, Netanyahu could call their bluff and go to these places, and if they backpedal, then it would undermine the ICC's authority like you said. But Netanyahu would have to call their bluff for that to happen, or they would have to do an about-face before he arrives.

But until then, I would suggest that even the fact that just two well known western democracies quickly backed the ICC's authority (regardless of what they thought of the ruling) just gave the ICC more authority than it ever had before.

They're making noise, but they will absolutely not act on them. That would be a career ending event for many political figures in both countries.