The crowd sourced training analysis confirms the long held conventional wisdom that double position training has about 70% the speed of single position training.
Now, two position training can be useful for getting a crew of decent players trained up, and saving the money that you would otherwise need to spend to buy them off the TL.
But if you really want to train top flight players, you'll want to do mostly single position training so that you're players increase their skills at a sufficient rate relative to their aging process.