This stretch that you're putting a ton of emphasis on. What position was he playing for the majority of it? He was getting significantly more ice time than he's averaged in years prior. Add Jack Hughes and a significant UFA and I don't see that happening again.
I think a big part of why I don't see his offense thriving in New Jersey has to do with the opportunity he's likely to see moving forward. But I also don't see a 60 point center waiting to break out here either. So to answer your question, both.
If Devils fans see this player as the guy who's 'sheltering' Jack Hughes from tougher assignments, I see his offense being stifled. But I also see why the Devils value him as a part of their roster.
He's always played center in the NHL. His ice time went up somewhat, but an extra minute or two is not that significant of an increase and certainly not enough to justify it driving his increased offensive production. Especially when you consider he was usually not playing with very good linemates.
I get what you're saying that he certainly had more of an opportunity to get top 6 ice time the past season or two than he may going forward, but his continued progression should more than offset that.
Zajac and Nico are also very good defensively, so it would not just fall on Zacha to shelter Hughes from tough assignments. It'll be interesting to see what the Devils do with the lineup next season - would they really consider having Zacha or Zajac as a 4th line center when all 4 are healthy or does one of them get shifted to wing when that's the case? Many NJ fans assume that Zacha takes over for Zajac eventually as a 3rd line shutdown center, but I think Zajac still has a few more good years in him.
60 points is aggressive, but I certainly think he could be a 40-50 point player in the next year or two.