Oh, you mean roads like the D&H, the D&M, the LIRR, the Green Bay and Western, the Rutland, the Susquehanna, and many others? Todays Arkansas and Missouri, GVT, Lake States, and LA&L/WNY&PA still rely on Alco power.
Alco made a good product, but in the long run, EMD and eventually GE put Alco out of business because they were bigger, had deeper pockets for R&D, and could offer financing (GMAC, GEC etc.) that Alco couldn't offer. Also, Alco was dependent on GE for their transmission equipment, as were Baldwin and FM in their final years.
I'd like to see some real proof of your statement that railroads having Alcos needed to have EMDs or other brands of locomotives to back up the Alcos. And since I don't understand your comment on the H12-44, I'll say nothing-