American Steinways would be preferred by most American pianists than the Bösendorfer. But there are others they might prefer if they had any experiences with brands like Fazioli, Grotrian, Bechstein, Steingräber, Förster etc. Under the second ownship of Steinway, CBS, there were deep pockets to withstand the loss for over twenty years. And according to books on the subject, you will find that aside from being good pianos, there were rigged contests, clever endorsement packages etc. that helped to obliterate the other American manufacturers before the financial backing of CBS.
In the past, under CBS ownership, nine foot Steinway grands were placed in all the major cities, given to the dealers for the express purpose of renting them out for concert use. It would be suicide for a traveling artist not to be on the list of Steinway artists. In exchange for being on the list, they were not to publically endorse any other products. Even if they preferred an obscure instrument from Europe they would not find 20 nine foot grands, let alone one in NYC, or 15 in Chicago or 6 in Detroit to choose from when touring those cities.
In the past before World War II, Steinway was much lesser known in the world concert circuit. There were over 300 Bechsteins and 300 Blüthners in Europe in their concert rental programs. All were lost after the war. Most factories were bombed and had to start over. Steinway, being American, and having a factory in Hamburg got the gigantic leap forward in becoming in the forefront.
The concert grands are still being produced to concert standards. It's often the smaller ones that are not in the same league as their larger ones.