The two positions are not mutually exclusive: massive economic disruption allows laws intended to promote equality to suddenly succeed. Likely WWI & II made politically impossible things suddenly possible. For example, FDR's attempts at Keynesian intervention were either timid or blocked (like the National Recovery Act). During the war taxes could be used to massively raise employment (albeit making weapons) and prime the pumps for the post war era.
And it is difficult to identify the motivation behind every piece of legislation but the Roosevelt administration, Beveridge, LBJ and others often acted with the clear intent of creating greater equality. And, as I think you point out, did things that would have been impossible before the wars.
And it is difficult to identify the motivation behind every piece of legislation but the Roosevelt administration, Beveridge, LBJ and others often acted with the clear intent of creating greater equality. And, as I think you point out, did things that would have been impossible before the wars.