The following comes from a “Is it just a Phantom” – David Wardale’s response to Herr Ebel published in Lok Report in March 2001:
“It should be noted that needle roller bearings were an integral part of the American Baker valve gear, and are extensively used on Walschaerts valve gear on Chinese locomotives, operating successfully in a rather harsh environment.”
David has also offered the following response to the same question: “Baker valve gear is primarily rejected because it has too many pin joints (more than Walschaerts, check for yourself).  I suspect it is also heavier.  Obviously opinion was divided even in America on the relative value of Walschaerts and Baker as some of the better railways (e.g. the Pennsylvania) preferred the former to the end.  The only advantage of Baker that I know of is elimination of the sliding link/dieblock, and as you rightly surmise that problem is dealt with by mechanical lubrication as on the SAR 25 Class.”