It's quite common for a small amount of Petite Sirah (5-20%) to be added for structure and improved color. Some Zinfandels can be pretty light. This is pretty typical. Ridge "Lytton Springs" Zinfandel is legend (and a personal favorite) and it has petite sirah, carignan, and Mourvedre inter planted in the vineyard and it all gets picked and processed as a field blend. They have a story board at the winery where they have had each vine in the vineyard identified. Apparently, when originally planted years and years ago, it was planted as "mixed black grapes" which turned out to be mostly Zinfandel with some others mixed in.
But it blends well with many other wines, and I make a Primitivo(basically zinfandel)/Syrah blend every year that I like as an outstanding casual food wine.
But when blending, for me it's always an accident. What ever is left after main bottling gets blended together and I've never had one I didn't like. My 2020 blend is a mix of primitivo(50%)/barbera/sangiovese/tiny amount of syrah. It's quite good despite the lack of precision and I think most "Red Blends" are made this way. After all that hard work, I wouldn't want to throw any out, so leftovers all go in the tank!