Big spenders already do not bid on google directly, but balance budgets automatically between multiple platforms and channels base on performance

Depends on the big spenders, tbh. Internet native brands are more likely to do this, but larger more staid companies will take a lot longer.

> but larger more staid companies will take a lot longer.

I still believe large spenders already advertise on multiple channels and balance budgets based on performance.

Sort of. It really does depend on the company and how they're set up. Like, brands using agencies or more non DR advertising only update on marketing mix models which are much slower.