Hi intufreecad, welcome here.
Why say "But ... also" ? Better say "And ... still"I think the solutions with sketches are very elegant. But there is also another way, working only with part workbench and draft workbench.
Very nice example of CSG using Part WB. I could have extrude my sketch out of a body with the Part Extrude and say I used Part WB, but IMHO it won't be the real sense of it. Your example definitely is.
Hmmm... Are you French ? (Looks like most CSG modelers are)
Here we could discuss the meaning of "parametric". But yes, your model is tunable.The power of freecad makes that even such solutions stay parametric.