I spend a lot of time studying blockchain and Ethereum and wanted to clarify your remarks.

  You need some sort of cryptocurrency for this as
  microtransactions don't really work in the legacy
  system.

Yes, you're right: Ethereum has lower transaction costs, lower non-monetary transaction costs, and ERC20 tokens are interoperable with other Ethereum-based services.

  Also by using their own token they can boot strap
  the ecosystem cheaply as they can mint the tokens
  themselves with the value accruing later after
  network participants are onboarded and transacting.

This is a common sentiment that I believe is incorrect: if a project could use ETH or USDC instead of its own token, but still function correctly, then that token is malpractice. Such tokens are a blight on the blockchain industry.

Projects like Augur and MakerDAO must have their own token or they wouldn't work at all. Augur and MakerDAO have healthy token economics.

I'm not an expert on BAT token economics, but I believe Brave would have been much better off using ETH itself or a stablecoin. afaik Brave's microtransactions don't require BAT to work and that makes BAT a bad token.