ahern. oops.... my question was about the use of arrowroot powder in the recipe. I always think of it as a thickener. Is the amount (60 g) correct?

It is there as a starch -- a necessary balance for all the flours to get a good result. Don't omit it and disregard all prior training of it being a thickener. In other circumstances it absolutely is a thickening agent and likely performs an overall service in the recipe that is analogous. All GF flour blends require some starch to be successful.

The arrowroot might be there to bind to the water in the bananas and lighten the texture of the bread, otherwise, the bread might have a dnese,gummy texture. It's just a theory, but I think that's why there's 60g of it.