Keep in mind that choosing crew skills is not completely binding. You can unlearn them / learn new ones at any point. As for your question, yes, as of now Armstech/Armormech are essentially useless, as you obtain the gear you need as you quest. I am an Armormech, however, just keeping my fingers crossed that eventually BioWare will give us a nice buff. Biotech is really good for leveling, as it gives you essentially free medpacs/stims for life. You should NEVER, I repeat, NEVER die as a Mercenary with unlimited medpacs. I say go Diplomacy. It will provide you with the ingredients you need for advanced recipes as well as companion gifts to keep your crew running faster, and unlock possible quests for them. Slicing just isn't efficient enough, IMO. Hope this helped :]