If nothing else it adds the same sort of inner turmoil that ex-SHIELD agent from an earlier episode had when she was stuck with the implant, in that SHIELD's done him no wrong but thanks to the killswitch he's going to have to do things he doesn't necessarily want to do. If it were all crammed into the first episode there wouldn't have been much room for establishing the SHIELD team (and likely would have left Petersen a fairly one-dimensional character).
Disagree.
For one, we don't NEED that turmoil. We already had it with the ex-agent in that earlier episode, and frankly I am getting a little bit sick of all these people outside the flower girl seemingly getting put into the "program" against their will. It would have been way more interesting to have Peterson/Deathlok almost happy for his implants, even if he knows it gives the leader control over him, just because they help him battle SHIELD to reclaim his son. It could have been built up to a point where he changes his mind and grows as a character, instead we go through yet more "He has to do bad things even though he is a good man" bullshit we have gotten from multiple characters in the season so far.
For two, all they would have to do in the first episode is change one thing about the ending, and don't have his little "joining SHIELD" arc. Basically cut out what ended up being worthless fat (he was a member for one episode, big woop) and get to the meat of the origin, a man given great powers is taken by a greater force and put into service. It wouldn't take away from the SHIELD origin development, even though what we got was already dry.
And lastly, he would only be "one-dimensional" if they just made him go "RAWR! DEATHLOK KILL" and nothing else, but his motivation will always be that he has gone made from his ordeals and "only wants his son back", which could lead into major character growth down the line. Right now he is just flopping from "good, bad, good, bad, LAST MINUTE GOOD!, wait now slave bad". Honestly even if they did make him one-dimensional, there is nothing wrong with that. This show has way to many characters as it is, all of which they are trying so hard for me to care for that I find myself caring little for any of them.