I've never seen a more wrong opinion about beetles.
A beetle snipe didn't set you back 4k mass when you could load up 4 onto a T1 transport and kill a full HP ACU 5 minutes into the game. You're not getting flak this early unless you're paranoid and immediately rushing T2 or keeping your ACU in your base the whole game. Flak doesn't work 100% of the time either. Mercies are a bit different in that people don't counter them properly, the best counter to mercies is scouting and suiciding in a handful of inties to kill the whole lot in 1 pass before they leave the base. Unlike a tanky transport, there's no defending that.
Unlike nothas, beetle drops can be stealthed and you can drop engies with them to steal the mass. I used to steal T2 and T3 mexes that way, of course it's much harder now with halved reclaim speed. It's also more cost-efficient than nothas assuming old beetle damage and much harder to stop once they land. Just like arty drops really.