-1 range on towers could potentially be introduced in random map scripts, to not break scenarios. but inconsistency over different maps and scenarios is not healthy for this game (arina already confuses so many players)I realise this won't happen but...
You could have a (food) upgrade that enables ungarrisoned towers to fire arrows. (They would still fire arrows when garrisoned with villagers/archers.)
Defensive towers would still be viable without the upgrade; the defender only needs their towers to fire when they are attacked - at which point they would normally want to garrison their villagers anyway. The tower rusher would either have to research the upgrade or commit units to maintain a garrison in all/most of their offensive towers.
Alternatively, watch towers could just require the guard tower upgrade to fire arrows without a garrsion.
Btw, I've heard the argument that reduced range for towers would break scenarios, but (as someone who has played very few) are there really so many that would require massive change due to something like -1 range for watch towers. Even a completely tower based scenario like ancient tower defence would be playable, just slightly more difficult. But the increased cost of towers probably is the bigger change for this scenario.