Preach it my man.
I get why people want a bit more certainty than Sully provides but the truth is line juggling is just an NHL norm and there's good reasons for it. For one thing, it's just necessary to deal with injuries and losses of form. For another, head coaches in Sully's position do need to be experimenting and seeing what may give them an edge come the play-offs, both in terms of working out the best combinations and working out injury cover. And to a certain extent I think it just helps keeps things fresh and players on their toes to never make things too settled, which is necessary over an 82 game grind. Particularly in circs like Sid and Horny. There's really no mileage in trying to make Sid like the pairing if he doesn't. Even if I thought Sid and Horny were unequivocally always the best use of the Pens' resources, I'd still be okay with changing it up pretty regular.
They're not though. I don't think we should judge the pair on last game where Sid wasn't properly tuned, and they were strong last season, but Sid's pretty good with a lot of people and probably exploits open games better with others, and there's reasonable grounds to think Horny can be a difference maker on the third line.