What's new here is the "opener" concept, which can complicate platooning, since the "bulk guy" is basically the starter, only he comes in some time after the "opener," and may not pitch with the same hand. A manager may be forced into making a platoon decision way early.
But platooning itself is as old as the advent of LH pitching. Which is to say, it's always been around. Tom Kelly used to use Mike Pagliarulo and Scotty Lieus at 3rd. Earl Weaver platooned. Casey Stengel. Etc etc. It's an age old way to try to squeeze a little more offense out of a position, since the platoon advantage/disadvantage is real, and almost universal. If your roster was big enough you'd ideally like to platoon most EVERY position.
Your issues with Gallo are another issue entirely. And you should have the same, or worse issues with Luplow, BTW. Luplow is, if anything, a worse hitter than Gallo and a worse defender as well.
The problem is having Gallo and Luplow as your choices, not Rocco trying to maximize his poor options.