Just to be clear - Boyle scored 8 ES goals in 67 games.
In 2016-17, the 4th line centers were Josefson, Coleman, and Fiddler - these players combined for 3 goals. Even if you want to count Blandisi and Kalinin you still only get up to 6.
In 2015-16, Gionta scored 1 goal.
In 2014-15, Josefson was used as the 4th line center - he scored 3 ES goals.
In 2013-14, Stephen Gionta was mostly the 4th line guy - 3 ES goals
We can keep going like this back through the years, but the truth is that the Devils haven't gotten 8 ES goals out of their 4th line center(s) in well over a decade - maybe 2003, definitely 2002 if not 2003. Boyle looks awkward sometimes. But he scores goals. When that stops, so does his NHL career.