Yeah that's the point Drop. It's the choice of style. Basically like MarineKing. If you're going mass infantry then exploit your mobile army to take way more expansions. The protoss then has better units and more tech but terran hopes to overwhelm him with numbers. The way the terran sniped the colossus is simple. Double pronged attacks.
The colossus ball has to stick together. So the terran did things like attack the 2nd base when protoss army was on the ledge at the third base. The army would move down the ramp and the colossus on the cliffs start to hit the terran attack. Then another group of marauders would come in from the xel'naga tower and gold ramp stim and kill as many colossus as they could. Terran did this a few times then toss splits his army a bit. Then terran makes one big attack on the weak side and uses a small force to poke at holes from the protoss army moving to deal with the big attack.
This whole style is basically what MarineKing has specialised in. Hitting weak points. Attacking multiple places at once. Forcing the opponent to stay in his base. And all the while MarineKing expands a lot. It's almost like a zerg style. Like mutaling. It doesn't do super well in a straight up fight but just by constantly harassing zerg can get up more expansions and get upgrades and the tech to get units that counter colossus better.