Ren watched a bit of the battle before he intervened. If it was the normal Valdel he would've found a way to overcome such a situation, but what Ren saw happen was different. He had seen how Valdel had lost his cool and attacked. He was the one who had trained Valdel from childhood and knew most of his skills so he was sure that this was something that he could've dealt with. Yet this time something different happened. Could it be that the time they had been separated from training Valdel had changed? It has been a couple of years, so there might be things that he didn't know about, but the current Valdel was nothing but an embarrassment.
The current Valdel was no longer purely seeking strength, nor was he blindly pursuing his so called justice. He was changing, it looked like he was being devoured by some unknown greed.