> I generally agree with this sentiment--the biggest value blockchains provide to decentralized applications is an inimitable 100%-replicated log

You're coming at this backwards. Once you have the most valuable cryptocurrency unit of account, you have the most security and the highest availability log in the world. On that basis, you can do just about anything, e.g. sidechains or payment channels.

A "highly replicated log" is a prerequisite of that, and Bitcoin is currently winning that battle due to first mover advantage. Hence, anything can be built on top of that basis.

If you have small competitor to Bitcoin that aims to do more, it's more valuable for the majority to snipe the features from the small competitor and make those features available denominated in the majority owned asset.