Yes. Possibly some are more finely ground than others - I have found them
suitable - I mix them with gum with a pestle and mortar, but don't grind
them dry. I know some others in the UK who have done this too and got
good results. I wonder if it is the particle size or the mixing with the
gum that causes the problems you had.
Generally I have found Winsor & Newton colours no better than the cheaper
Rowney range - but there will certainly be some exceptions. I have found
it a lot easier to get information about the W&N range - for example on
light-fastness, toxicity... It's a few years since I was active using
gum, but as well as pigments I also used tube colours from W&N, Rowney
and Talens (Dutch).
I suppose my point is that you can't rely on the contents of a tube
saying, for example, 'Yellow Ochre' to be the same either from different
manufacturers or even from the same one over a period of years - so you
may find suddenly your favourite colour no longer works if you rely on
tubes. Powdered pigment is also a lot cheaper.