Why should we assume that tiny houses would be insulated beyond the bare minimum? Yes, the current trendsetters care about the environment, but nothing is preventing them from building well-insulated apartment blocks.
Soundproofing techniques are well-understood and not horrendously expensive (of course, many builders don't bother because it's not worth the cost, from their short-term perspective). And separate buildings in close proximity still allow plenty of opportunity for sound to carry—again, unless soundproofing has been performed.
You seem to be making the assumption that tiny houses will always be built well above minimum code requirements, while apartment buildings will not. If tiny houses really go mainstream, that will no longer be the case.
Soundproofing techniques are well-understood and not horrendously expensive (of course, many builders don't bother because it's not worth the cost, from their short-term perspective). And separate buildings in close proximity still allow plenty of opportunity for sound to carry—again, unless soundproofing has been performed.
You seem to be making the assumption that tiny houses will always be built well above minimum code requirements, while apartment buildings will not. If tiny houses really go mainstream, that will no longer be the case.