Old or solved topics may go to bottom or to a 'archives' tab, but replying should be easy. Disagreeing with a past solution must be the easiest thing ever.
No past technology with classic talk pages involves closing right of users to reply, other than archival. Nothing ever makes replying harder.
You please don't make replying harder, either; archives can exist, but only by means of a topic going old/inactive, not by means of a topic being thought as "resolved" by a single contributor.