Without any comment on quality, it's helpful to keep in mind that P&C was bought just before the war and retained its own identity (in terms of unique dies) with some if not many tools throughout the war. By 1948, that had changed. Most of the tools (incl screwdrivers, hammers, pullers, adjustable wrenches, DOE wrenches, and the boxes and toolmobile) in the 1948 catalog are Plomb designs, although P&C was still making their famously round-shanked DBE wrenches. In 1953, those were gone. If you look at the 1939, 1948 and 1953 P&C catalogs, that evolution is visualized right before your eyes.
The one area I'm not sure of is the drive tools. Did Plomb ever make open-gear style ratchets? In 1939, ALL P&C ratchets in ALL drive sizes were open-gear style. (They also made a really cool one-hand speeder - unique as far as I know, without a full swing. The shank had a slight wiggle in it, just enough to get some cranking action going with some pressure from one hand. I think Rileysan may have one.) In 1948, that unusual speeder was gone and the 1/4- and 1-inch ratchets were clearly Plomb ratchets. But, surprisingly, the 3/8-, 1/2- and 3/4-inch ratchets were still all P&C open-gear head. Same situation in 1953. I'm under the impression that Plomb ratchets weren't, so that is also some independence, and it may extend to other drive tools I have not bothered to scrutinize in as much detail. Someone correct me if I'm wrong about that.
As for quality, I don't think P&C was ever advertised as an economy line Plomb brand. In 1939, when they were still their own entity, they used the slogan, "The Best Tools That Money Can Buy!". In 1948, that was still their slogan, and the only reference to Plomb was a parenthetical qualifier under their address: "(A Subsidiary of Plomb Tool Company)".