Блендинг - это заявленный функционал табло. Если у вас невозможен джойн, т.е. источники которые не поддерживают его, данные грязные, и нет возможности сджойнить. GA тоже не поддерживает cross DB join.
You want to combine data from different databases that are not supported by cross-database joins.
Cross-database joins do not support connections to cubes (for example, Oracle Essbase) or to some extract-only connections (for example, Google Analytics). In this case, set up individual data sources for the data you want to analyze, and then use data blending to combine the data sources on a single sheet.
You can use data blending when you have data in separate data sources that you want to analyze together on a single sheet.