There's always an added risk with signing a player with a history of injuries. For ICT the risk worked out brilliantly with Dargo, and even Niculae came good after a slow and unfit start.
I agree it's all about risk and reward, but the assessment has to be made at the time, without hindsight, and your comparisons seem a bit unfair to me.
It's easy to see why OTJ was signed on a good wage - experience of playing at a decent level over many years, and an international to boot. A risk worth taking? I don't recall anyone saying anything to the contrary at the time.
GMS on the other hand had never played a competitive game of football in his entire life. ICT took him for a test drive and he broke down. He was clearly talented but very high risk. I'm pretty sure he would have been touted round every pro club in Scotland that summer, but nobody signed him, not just ICT, nobody thought he was worth the risk on the terms he was looking for at the time.
Dundee Utd only signed GMS the following season, after he had eventually proven his ability and fitness with Airdrie. Should we have looked at him again at that point? He was certainly worth the risk by then but we are pretty strong in that position and had other signing priorities.
There's always a degree of luck with these things, but it's perfectly understandable why all parties did what they did and didn't what they didn't. It's also perhaps a bit early to be concluding or implying who was the better signing - there's a long way to go, and Saturday was GMS's first 90 minutes this season - OTJ has at least managed two full games!