Sorry, but this is just all wrong. Like the exact opposite.
You don't bench players for production, typically. You bench players for commitment issues, or attitude problems, or lollygagging.
You also bench the incomplete new guys because they are incomplete. You have a chance to fix those issues before they become set in their ways.
You also bench guys because it will make them better. Benching Glendening or DeKeyser isn't going to do much good. They seem to be doing the best they can already. Mantha can be better.
Sheahan has to play at 100% to stay on the roster. Glendening too. Helm. DeKeyser. Jensen. Zetterberg. Whether that's good enough or not is an entirely different discussion. Mantha doesn't get to put in 75% effort, even if he's out producing everyone.
This whole Mantha benching thing has just brought out so many people and so many opinions that just don't seem to be based on reality.
Your entire argument is based on the notions that:
1) Players shouldn't get benched for extended bad play.
2) The majority of this roster hasn't been guilty of at least occasional bad effort.
I disagree with both.
If a guy plays like trash, even if he's giving 100 percent, he needs the occasional break. And I can count on one hand the players that haven't had at least a couple bad effort games.
Again, benching anybody to send a message is fine. But when 90 percent of the roster has at least occasionally been both lousy and lazy, the wrath needs to fall on both the young and old. Not necessarily equally, but there isn't a single player not named Zetterberg that hasn't deserved to sit at least ONE game this year.