I agree that UBI is fundamentally broken because it disincentivizes productivity by gifting everyone a fixed amount for simply existing and producing nothing of value.

This is based on the assumption that people will just sit around and do nothing. What's your basis for that assumption? In fact most trial UBI experiments see the opposite happening.

And even if you still thought UBI was "broken" (which it's not) it's not as broken as capitalism where technological unemployment is growing thereby removing purchasing power of the consumerist class. Without people buying stuff, capitalism falls in a screaming heap. UBI makes eminent sense if you believe that capitalism has any future.

Regarding your idea for inflation based UBI, sounds interesting. As long as it couldn't be gamed. What do you think about the possibility for gaming such a system?