I think your raised concern regarding usefulness for some communities is completely valid. I’d also be happy with this being an optional setting that admins can set for the entire site if they choose to.
E.g. default the lock symbol remains for all locked and archived topics, and there’s an option for those community admins who’d like to, to change the symbol for archived topics within the topic list. I’m sure code-savvy people could already achieve this by making their own modification, but a drop-down setting might be more userfriendly for those of us who suck at CSS.