Max gained a lot of insights from his battle against Rudra as although he could not prove his full potential to his brother, for the first time he realised the areas which needed much improvement from his end.
Neither from fighting monsters, nor from fighting average opponents could Max have ever realised the shortcomings of his techniques, yet a single spar against his brother made it clear.
There was a lot of room for improvement for him and although there was a gap in strength between him and Rudra at the moment, Rudra had already finalised his style of fighting while Max had only laid down a solid foundation.
Max was in a unique position where he still did not have a signature fighting style which he called his own, yet he was able to progress this far as a successful warrior.