Watertight models are no problem with Cinema 4D. If you design models and not only prepare other peoples models for printing Cinema 4D is a good choice. If you mainly clean up designs, I'd look somewhere else.

Cinema 4D makes use of objects, which retain their parameters. So you can change or reuse your design easily. Deformers allow you to modify objects without the need to give up option to edit the object parameters.
There is a number of cloners that allow you to multiply objects by arranging them in grids, circles etc. and on the surface of other objects. In addition the position of the elements can be modified randomly or by functions. Always retaining parameters. One of those factors is the number of vertices. So you can adjust the polygon count to your needs.
There are generators that create particles and animate them. You can use them to create/move your objects, have them animated until you have the effect you want and copy the geometry at that mark. Great for creating clouds, exhaust or nuke mushrooms and much more.
The same can be done with cloth simulation and/or physics.

You can also work on polygon level, but than you will have to turn the object in a set of polygons, giving up the ability to change the object by parameters.
One nice option when you work with polygons is sculpting.

Cinema 4D has some quirks and sometimes it may expect you to do things differently, but I guess that is true for all applications, as is the fact that there is a learning curve.

I never had a case of a not watertight model.

As I said at the start, if you mainly design Cinema 4D is a good and, if you can adapt to it's way to do things a very good, choice, but if you do mainly cleanup look, I'd look somewhere else.