I haven't seen Bobcad since version 18 so I don't know what they've done in it.
OneCNC is fairly basic, its not parametric, so you've either got to draw it correctly the first time or draw it again correctly The general method is to accurately lay out some geometry, which, to the best of my recollection, is/was similar to old Bobcad18. Not identical of course, but similar enough that switching from one to the other was not much of a jump.
Then if you want to go to 3d, then you begin extruding that geometry or adding/subtracting simple solids to build a model. Old Bobcad18 didn't do anything with surfaces so I cannot compare the later versions to OneCNC.
We are able to select any face of a part and begin doing drawing/modelling on that face. If you are used to mentally working from a known datum or datum line, its very straightforward to model up a part.
The 3d modelling aspect takes a bit longer to get used to, but that is just the nature of the beast. That is to say, there is a certain set of rules that you pick up along the way, mostly to do with learning to do what is mathematically correct. For example, let the geometry make its own intersections, so that the trims are perfect. Make sure surfaces truly intersect before you merge them. The kind of stuff that leads to perfectly sound models, that will then behave themselves when you want to do further operations upon them.
OneCNC is a hybrid modeller, so you can work with geometry, surfaces or solids. It is kind of nice to have that flexibility when you get used to it.
The best answer I think would be for you to contact OneCNC sales and get a tryout that you can work with yourself. There is no other way to know whether your expectations will be satisfied