Jansen's underlying numbers don't show any real batted ball luck, in fact his numbers earlier in his career consistently showed terrible batted ball luck compared to the results. I'd rarely ever bank on a player repeating a 140 wRC+, but it's definitely possible that Jansen could reach that. He also projects as a 120 wRC+ hitter, which is really good.
w/r/t second base, projections show Cavan at 106 and Whit at 98, one is above average, the other is a tick below average, neither is "below average hitting by far".
Bo's career wRC+ is 127 and 120 is the lowest number he's put up in any season, he swings wildly, but he gets amazing results. In a down year, Vladdy still posted a 134 wRC+, and projections have him at 166 (whether or not he meets that largely depends on his launch angle, IMO, so hopefully he's improved that a bit during the off season).
I have absolutely no concerns about this team scoring runs, and I think the pitching, defence, and base running have all improved.