在美国英语中，通常使用as...as...引导让步状语从句。例如：

As cold as it was, we went out.

= Cold as it was, we went out.

尽管天气冷，我们还是出去了。

As successful as he is, he is not proud.

=Successful as he is, he is not proud.

他虽然成功了，但不骄傲。

你的句子：As comforting as it was to be Garrett's idol, it didn't diminish the horror of being Basketboy number nine. 等于说：

Comforting as it was to be Garrett's idol, it didn't diminish the horror of being Basketboy number nine.

在让步从句中，其中it 是形式主语，to be Garrett's idol 是真实主语。