That's over a 4 year sample size with all the attendant highs and lows, not a ~50 game sample size with Kessel where even Sheahan's biggest admirers admit they haven't worked well together.
Yet his point stands. Production (
outside of power play) of a good 2nd line center in any given season last 4 or 5 years (centers around Top 40-45 range) was around 0.5 PT/G (40 points per full season pace). Production of a good 3rd line center (Top 70-75 range) was around 0.35-0.4 PT/G (30 points per full season pace). The list differed from season to season because of your aforementioned highs and lows of individual players. The question with Sheahan is not whether his performance so far is enough but whether he can keep it up (and especially in POs). Because while you can try to get better on that 3rd line center position, the realistic options won't give you significantly better scoring output.
You're advocating limiting our match-up options considerably. And if we stop splitting up our superstars, we ain't gonna be getting .40 ESP/G from RS either.
He is producing like a lower-end 3rd line center playing regularly with Phil Kessel.
About that:
Sheahan with both Guentzel AND Kessel: 116 min, 4 pts, 5-6 GF-GA, 47.9 ZSR
Sheahan with just one of Guentzel or Kessel: 81 min, 1 pt, 1-5 GF-GA, 26.8 ZSR
Sheahan without them: 380 min, 13 pts, 18-16 GF-GA, 28.7 ZSR
He seems to be perfectly capable of producing at 0.4 ESP/G without them on his line. In fact if PIT won't get another scoring center (like Miller or Anisimov) loading up the top6 seems like a better idea.