I will not presume that I am an expert at this game or RTS in general. If someone can tell me a counter to an enemy building mass catapults with advanced radar other than beat them to it, please do! But based on the last match I played the catapults coupled with advanced radar can be built near an enemy base and harass to a level that is near impossible to respond to. I threw everything I had against it and the weapons AoE effect wiped out groups, those that did hit it did a negligible amount of damage. This resulted in the enemy building a line of catapults nearer and nearer to my base wiping out my economy and forcing me to surrender. Again, if I am missing some valid strategy that is great, just highlight it for me, I am sure this tactic will begin to be exploited soon. The enemy player even admitted the tactic seemed impossible to counter and OP so that is never a good sign.
Balancing isn't really an issue right now. I'm sure Uber can just straight-up nerf the Catapult's Damage or AoE, but that is a temporary fix. I haven't had much experience with the unit, but a large minimum range might solve this issue, that way it can be successfully rushed and blown up. Bombers would probably also work wonders, assuming they didn't faceplant into the rounds.