I'd be shocked if most of the Bruins didn't show notable improvements in these kinds of stats and their overall WAR % after the season they had, especially a young guy like Frederic who only has a small prior body of work which will make an exceptional year stand out even more. I don't mean to wholly write off Freddie's development on that basis - he definitely took steps forward in his game last season and became a more rounded player - but some of these numbers are inevitably also going to be impacted by the overall performance and win rate of the team for which Trent of course deserves some but only partial credit. There's most likely going to be some amount of downwards correction this coming season, and that's equally as true for Frederic as a more established guy like DeBrusk unless he puts together a really exceptional individual effort.
That said, again I think there's no question we saw a maturing in Freddie's abilities last season and improvements in his playmaking, defense and finish. I don't get all giddy about the 17 goals but they're not to be sniffed at either. Against that there's equally no doubt that for whatever reason, possibly fatigue, he flaked out in the last part of the year - just 3 points in his last 13 regular season games and then, when it matters most, a poor playoff performance. But while not ideal I think that can be excused given he's still relatively young and, on balance, as a homegrown guy who's delivered on at least some of his promise and who I think still has some upside, especially in a different looking team where he should get some more opportunities to further prove himself, I'd rather the Bs retain him. He's not indispensable and if a good trade offer came along you'd have to look at it, but the default option should be to stick with him for now.
As a couple of others here have said, more than anything he needs to pin down exactly what kind of player he wants to be. Too often he seems to get caught between being one thing or another, and then winding up ineffective at both. I actually don't think the scrapper/agitator role really suits him, and I'd rather he just focus on being more physical during the general course of play while still looking to make smart plays offensively. A guy like Brady Tkachuk landed 242 hits last year, Frederic had 105. That's not nothing, but pushing that number up towards 200 in future would not only be a better use of his size but probably get him more engaged in the game in general.