There are always variations that prove the rule. Plenty of modern quilts use lots of pieces, but I'd say that there are large blocks of space (pieced or not) and often a lack of an overall grid structure in modern quilts. I think in many ways a lot of what is popular in terms of broken or disappearing blocks is modern, as are jellyroll race type projects.
Michael James was one of the first Modern quilters I was aware of, but that was back in the 70s and 80s, so in time line 40+ years ago.
https://en.wikipedia.org/wiki/Michae..._(quilt_artist)
I understand the desire to call them all "quilts" and that we are all "quilters" without further breakdowns. Having said that I consider most of my work to be "contemporary adaptations of traditional patterns". For me personally, quilts are a craft, that is a functional object. There are other people who do textile art in a quilted form. That doesn't mean both aren't valid or that they aren't both the same and different at the same time.
There are certainly design considerations between someone doing a yard or smaller wall quilt and someone doing a king sized bed quilt. Comfort and washability and perspective/point of view -- how far away from the piece do you have to be to recognize the design as well as things like sides/borders hanging down and being non-visible.
To judge art/quilts, you need to understand what it is the artist/quilter is trying to express and categories help with that. How can you really judge between an excellent Baltimore Album appliqued top or a exquisite Modern top that is pushing our boundaries/understand of what can be done with fabric and the work of machines or human hands.