既然你接受了嵌入式关系分句，为什么不能接受what引导嵌入式名词性关系分句，而要用不准确的插入语这种分析呢？

（原句）There has been growing anti-AAA sentiment in recent years, and anger at what many feel is increasing AAA interference in BBB affairs.

（改写句）There has been growing anti-AAA sentiment in recent years, and anger at the thing which many feel is increasing AAA interference in BBB affairs.

what=the thing which. which引导嵌入式关系分句修饰the thing.

夸克将这种关系分句称为push-down relative clause。

另外，你对嵌入式关系分句的理解不够正确。关系分句嵌入到many feel这个分句中，而不是many feel 嵌入到关系分句中，你将主次关系颠倒了。

你改写的句子与原句在意义上有所不同。