If anything, now that DAZ Studio 4 Pro is free it is less like those "free" things that you describe than the original free DAZ Studio used to be. Last year the basic Studio was free, but in order to "create content" and do more advanced tasks you needed to pay a not inconsiderable sum for upgrades—to Advanced and Pro. This is no longer the case, so you are getting a formerly "not free" program for nothing, rather than a shoddy made-to-give-away thing. That makes it a different paradigm, I think.

Of course there are costs attached (as you accept) because you will buy content, but that is true of any paid-for program of this kind. You could say the same thing about a free artists easel—you will have to buy, and keep buying, paints, brushes, paper or canvas if you want to use it for its intended purpose. (Although, unlike paints, your 3D materials are not consumed.) However, that is all you will be required to pay for, and of course, you need not buy any of these from DAZ (although you likely will—that is their gameplan).

None of the paid-for plugins are essential, and in any case, they are created by 3rd parties, and DAZ may not necessarily benefit from sales of these (e.g. Reality).