My opinions, for what they are worth.
He has recruited JC talent in the past so this was not a new concept. I think he was told he had enough time to build it with good recruiting and not a quick fix of hit and miss JC. Yea, it is easy to remember the ones that made an impact but others did not and they don't stick around long.
The team was fragile when he came in, duh. He kept Armstrong as the QB and bringing in a JC was the only option and the team would have been even a bigger mess than it was. The cupboard was completely bare in that area. Go with the upper class man, adapt to his talents which I think he actually did. It is just taking a long time and he used a lot of patience getting new talent in the loop. Again, I think it was due to the fact he was made aware that there was no immediate danger there and he needed to build it correctly.
The assistant coaches was a big deal. Some of the best bolted. If memory serves correctly the DB coach already on staff didn't get paid as much as new assistants and left. I can't see why everyone thinks Williams X 2 are so great. Maybe they are good recruiters, maybe they are good coaches but I personally don't see a great product from our WR's and DB's right now and these are highly regarded kids. Good talkers but not so great of producers.
Riley understood the culture of Nebraska just fine. He knew it was known for tough, smash mouth football and all of the traditions. He thought he could implement his pro style in a few years he would have the pipeline starting to fill up with talent. While better, it really never met the expectations of too many fans who just want to run the option and run the ball 9 out of 10 plays. I could see what he was trying to do offensively and where he was going, he just isn't there yet. A transfer QB (there is almost your JC) and two young guys is a start that he will point to.
I just feel like Riley made some bad moves and then reacted when things didn't go well. Hughes was a failure that set us back and now a change in D that is not going too well. Its like he thinks if he makes enough changes and tweaks, it will look good and it will indicate a willingness to change and made progress. It was like he was looking for quick fixes while all along, doing things for long term solutions.
There is a good stockpile of talent, but not great by any means. Whatever happens, the next few years could be good to high average.