I think Tsuna did develop a lot. The reason he went back was because of him meeting Emma. I'm not sure if you caught it but there was a lot of similarities between Emma and Tsuna. Tsuna also saw Emma as the guy he used to be. So of course it would cause problems for his new development. However, you guys just want Tsuna to wake up and be rambo. Silly.
Just because someone had the same personality the main character did from the start should not be a just cause for the main character to revert back to that state. If anything Tsuna should of been trying to help Enma out more giving him more encouragement since he knows what it felt like to be discouraged an made fun of. I don't want Tsuna to be rambo but what I don't want to see is Tsuna from the daily life arc in the current arc.