Part of the reason for that is probably that the former mostly happened in the regular season and the latter with regularity in the playoffs . He had a very respectable finals series against San Jose though in this rookie year though.
Slight overstatement. They fell apart against Columbus and Washington in 16-17 (although amply productive against Columbus, just the line got destroyed defensively), let in a ton of goals against against Washington in 15-16 but with the sort of stats that says I'd like to rewatch the goaltending (and were again plenty productive), were very good against San Jose, destroyed the Rangers, were decent against Nashville and a bit lucky with score effects and good against Tampa and a little unlucky with score effects. Aaand I just realised I forgot Ottawa existed and they conceded 3 goals there but statistically really shouldn't have. An on ice save percentage of 72.73% and letting in 3 out of 4 high danger chances is probably on goaltending.
Don't get me wrong - it has been an issue, and the greatest feats have been regular season, but there's been a lot of goalscoring from the line and a lot of series where's it worked. People's last memories of Sheary in the playoffs seem to be that Columbus series, wondering where all the offence went after NYR, and the goal vs San Jose. It leaves a lot of stuff out.
Very likely that they start out like that. After all that has been the progression in the past. A more concrete issue I have though - much linked to the above - is that Sheary works well with Sid when its North-South transition heavy hockey, which we really excelled at especially in 2015-2016 due to our speed advantage on everyone. We don't have that to the same extent anymore as the league caught on, and when we have to battle through, get dirty goals and win board battles, Sheary becomes a liability more so than pretty much any other player on the roster when he is played above his station/against better opponents.
I think the speed is less a skating thing and more a pace of play thing. If we can find our groove and force the game to be fast and open, Sheary will be fine, and I think we can still do that as long as we're not allowed a ton of clean zone entries in force. I've also got little concern about Sheary's ability to work a cycle with Sid (although I do about consistency) - it's simply the risk of getting penned in our zoned that bothers me.
I'd also point out Hornqvist over Sheary means the game is more likely to slow down anyway, which doesn't help us.
It will likely be just a few offensive draws per game where Sully can really get Sid out there against also rans. Opponents will consistently try to have their best our against our top6, usually Sid in primis, and Sully will rather play our 4th line against heavy opposition than the 3rd. So, there really shouldn't be that many 'hard minutes' left, IMO.
Looking at how it ran last time, probably true.
Ultimately, either Horny or Sheary should do well on the 3rd line in that kind of scenario, so it is all about which one of them is better with/for Sid's line to be effective.
For my money, Horny is one of those players who plays the same no matter the opposition. He doesn't have the talent or wheels to abuse lower level players through pure skill, and his wolverine qualities are about as effective against great players as they are against lower rung guys. With Sheary I think it is rather different, and he should benefit more from softer matchups relatively speaking.
Anyway... we will likely get to see both, and if our exhibition game against Philly is "for real" then that is a very proper measuring stick for deciding on the midget vs. wolverine strategies. Against Montreal it truly shouldn't matter either way, and if it does we aren't getting where we want to be anyway.
Slightly horses for courses based on the other guys there. I don't think you're wrong about Sheary theoretically being better equipped to abuse less skilled players, but Horny possibly buys the rest of his line more space to do it, and given they're maybe less likely to take risks and seek to collapse on the net, is more useful there.
But yes, we're probably going to see both. Guentzel is probably fixed on Sid's line, the other slot will be mix and match.