I wouldn’t say so. Just because it’s possible to find double rares, does not mean it is expected or realistic, and builds generally are not designed around them.
The chances of a double rare dropping are tiny. The chances of a double rare with the right affixes dropping are often astronomical.
If you want to you can try farming for them, but it could easily take tens of thousands of runs to find a specific combo of affixes. Less if you’re flexible on which double-rare you get exactly, but a fraction of a percent chance to get a useful combination of 2 rares.
See this thread for the nitty gritty calculations and a spreadsheet.
Also, even though rares are great and offer a lot of stats in total, bear in mind that the actual modifiers are smaller than the common affixes. So if you want to get a high OA on your Aether build, an “Of attack” sufix is going to help a lot more than “of Shattered Reality” even though the latter also gives you some extra damage and resistances.
All in all: if you find a double rare you can use, that’s great. But looking for them is a recipe for extreme boredom. And if a build needs double rares to perform well, it’s probably not that good a build.