I think the blame probably lies with a TMO, not Wayne Barnes. I think Lebel's is debatable, but I agree Baloucoune was a yard offside at the point the ball was passed. Ultimately, the TMO had all the angles and the ability to intervene but apparently checked and said the decisions were fine.
Ultimately you can debate decisions all day long, but it's not as simple as that. A try being given or not could completely change the mindset of the players and their response. Saying Toulouse definitely would have won had Lebel's try been allowed is dismissing all the different possibilities and variables that would have followed.
There is a second leg and it's only a 6pt deficit, which is pretty amazing considering how long Toulouse were down to 14.