The other shoe...tROAS too close to actual starves learning data
The other issue I see with the Google switch is that advertisers will have a historic ROAS they have hit which is well above the new target they set due to Google maximizing their performance previously. Advertisers will now try to set their tROAS where they have been hitting in the past and that will create a vicious cycle of Google being more conservative and participating in less auctions, which then starves the account of the data it needs. Many people have seen this over the years when trying to increase tROAS closer toward actual results, only to see the performance drop.