“Blending” has been going on for a while. Mostly due to American customer expectations than from any attempt to be daring.
The ubiquitous ‘glazed prawns with honey-sesame walnuts’ was a HK invention (I think; I don’t believe it started here) that swept through the Chinese restaurant industry incredibly fast. Now even Northern and Sichuan restaurants offer it, LOL.
My HK-born in-laws were going to Yank Sing on Broadway in the 1960’s, back when Mrs. Alice Chan was there every day. I met her in 1974 through them. She loved my husband and wanted to adopt him when he was 12.
Of course, now we wish his parents had been willing to give him up, LOL!
The dim sum menu was strictly Cantonese. There was no XLB. In fact, it was years before SF diners saw XLB finally introduced in the 1980’s when the first wave of ‘authentic regional Chinese’ restaurants opened, due to massive emigration from HK with Mainland China’s takeover deadline getting close.
Then it took more years after that before XLB started creeping onto dim sum menus. Cantonese were familiar with them - there are a lot of ex-Shanghai folks in HK - but you went to Shanghainese restaurants for them. Northerners don’t really have the extensive dim sum menus that Southerners do.