Are cloud or 'boneless' modular sofas actually comfortable long-term?

Verified-purchase reviewers consistently praise the initial sink-in comfort, but threads on r/furniture and r/interiordecorating repeatedly flag the same issue: low, soft back cushions that don't support an upright sitting posture, and gaps that open between modules with daily use. They're great for lounging and movie nights, less great as a primary 'sit and read' sofa.