It's worth noting that every NHL prospect on the Spitfires had disappointing production in 2016/17.
Brown went from 74P in 59GP in 2015/16 to 40P in 35GP in 2016/17 (0.11 drop in PPG from previous year)
Sergachev went from 57P in 67GP in 2015/16 to 43P in 50GP in 2016/17 (basically the same PPG from previous year)
Bracco went from 64P in 49GP for Kitchener in 2015/16 and 51P in 27GP in Kitchener in 2016/17 to 32P in 30GP after being traded to Windsor in 2016/17 (0.82 drop in PPG in the same year, 0.24 drop from the previous year)
Nattinen went from 71P in 52GP for Barrie in 2015/16 to 38P in 51GP for Windsor in 2016/17 (0.62 drop in PPG)
Knott went from 42P in 68GP in Niagara in 2015/16 and 17P in 14GP in Niagara in 2016/17 to 35P in 45GP after being traded to Windsor in 2016/17 (a 0.16 increase in PPG from previous year, but a 0.44 drop in the same year)
Addison went from 56P in 66GP in Ottawa in 2015/16 to 43P in 51GP in Windsor in 2016/17 (basically the same PPG as the previous season)
Plus a top prospect in Vilardi only had 61P in 49GP, when he is capable of much, much more
To summarize - Brown's production was disappointing for sure, but when you take into consideration that every single NHL prospect saw their production decrease or stagnate with the 2016/17 Spitfires, and the numerous injuries he had this year, it's definitely not the end of the world that his PPG wasn't as good as last season. This season will be much more telling for his future.