SMG's in general are a bit too strong past medium range. I like they shoot straight but combined with the high fire rate the damage drop off at distance should be a bit more aggressive on them to put them back in their niche.
https://docs.google.com/spreadsheets/d/e/2PACX-1vTvYgjDRT2tIhNxh6tZtOlXPovQwgL8dZOwkysY5n_nLHZESFwKZ3trx02VQ8Y-hAhUzOOHfLLR96bv/pubhtml
Someone on Reddit posted this chart and you can see even with the damage drop off the MP9 matches or bests all the AR's TTK at max range and is significantly better up close. There needs to be a bit more of a tradeoff.