I can't help but feel that shivs would be better than mecs. Mecs were little more than an additional character class. They certainly had their own interesting quirks, but really, they were just another member of your roster. I think that shives were always handled badly. They ended up being just another member of your roster(stealing experience from people who could use it, taking away a valuable roster spot, and not being particularly cheap or replaceable), but they shouldn't have been. Had shivs been weaker, but only required an equipment slot instead of a whole character slot, then they could have been the expendable bonus unit that they were meant to be. Or they could have been twice as durable with less armament and been a moving-wall/durable-scout. Or they could have been much more expensive and not taken a roster spot, thus taken a role as an expensive, if bland, upgrade to your squad. Or perhaps you could bring more than one per slot, so you could use them to replace quality with quantity. As it was they were just uninspired. Either they were better than your squad, in which case you really needed the experience and probably couldn't afford to waste coinage on something that would become obsolete, or they were inferior to your squad, so you were better off taking an expendable rookie that might turn into something valuable.
So much as I would rather see mecs-as-they-were than shivs-as-they-were, I think that is only because shivs were done badly...