When it come to how powerful nukes are, it really depends on the map. I don't have the time right now to do all of the math but this is the gist of it: SML is 16.5k mass, nuke is 12k. An SMD is 7.5k and anti-nuke is 3.6k. That means that the first nuke costs 28.5k mass which means that if enemy needs to build 3 SMDs then you are already ahead (Yes I know that nuke costs more power but I can't be bothered to account for that right now). This means that on any map that requires enemy to build >= 3 SMDs then nukes are basically always a good and safe investment. They are low risk and extremely high reward unit, simply a no-brainer in a lot of scenarios. Now consider maps that require only 2 SMDs, this means that either you are playing 1vs1/2vs2 which doesn't have major expansions or you are playing a turtle map with all bases clumped up. Then the nuke is not as strong but it isn't weak either. Remember that with 3 SMDs the nuke was basically worth it BEFORE it killed anything. But even if enemy's main bases are protected then there are still plenty of viable targets: expansions, armies, navy, forward bases etc.
If the range of the nuke would be reduced enough that you couldn't reach enemy's main base from your own it would just make the unit basically useless on those maps, especially in 1vs1 which I am not interested in (any smaller nerf siply wouldn't do anything either). The game is balanced around a set of competitive 1vs1 and team game maps. If you play on a map that strictly favors defensive play by clumping up all of the players together and doesn't encourage a lot of expansion either then you can expect the game to NOT be balanced. That is not to say that I think nukes are weak on DG, they are still viable. You just may not see 1 rushed every single game.