You are correct. All LEGITIMATE descents from William the Conqueror are through the female. William had 4 sons: Robert 'Curthose', Duke of Normandy, Richard, William II and Henry I and several daughters Adeliza d osp, Cecilia d osp Matilda, Constance and Adela (all of whom had descendants)
Robert had one legit son, Williiam Clito who died osp and three illegitimate children: Richard d osp, William disappeared from history after 1110 and a daughter.
Richard d osp
William II died osp
Henry I had two legitimate children: William d osp and Matilda (Maud), who married Geoffrey Plantagenet, through whom many descents come BUT he had many bastards to different mothers, including Robert Fitzroy, 1st Earl of Gloucester, Reginald de Dunstanville, Henry FitzRoy, Rbert William, Fulk , Gilbert and William, all of whom had descents, both legitimate and illegitimate, many of them male.
Descendants of these male descendants of William married back into other families of the aristocracy, so it is possible that there are male descents from William. I would love to see them....I don't have any male descents- all of mine are maternal. Sigh. LOL