dd.stevenson
Super KY
Generating playable content is, IMO, less work than making a published adventure (especially an AP) playable. Generating a fully detailed world down to the population of every small village is not. But a pre published world is not mutually exclusive from a sandbox you create yourself. In fact, this is the best combo in my mind simply because compelling, detailed world building is a lot of work. But I'll note it is completely unnecessary work -- you can have a great time playing D&D for 20 levels without ever really worrying too much about what the heraldry looks like or even what the days of the week and months are called.
Yeah, for sure.
I consider world building a different thing again than campaign prep, although there will always be some overlap. But the question of published setting or homebrew setting is orthoganal to the ideas of sandbox/railroad/procedural generation--one could just as well use use any of these with either sort of setting.