I'm not sure anyone claims he's untouchable or a lock to be in the top-6. And as much as you might think his salary would indicate that should be his role, the truth is 5m doesn't get you what it used to, plenty of 3rd liners who can can fill in occasionally in the top-6 make 5m or close to it. If he's overpaid it's by like a 1m or so.
Anderson has his strengths and weaknesses, and like most guys who are middle-6 players they rely a lot on their linemates to help them look good. For the most part we haven't been able to give him quality linemates that mesh with his style of game. I don't really disagree with much of your analysis although I would point out that in terms of being physical on the forecheck, measuring it via big hits thrown isn't a good way of doing so. The point of being physical on the forecheck is to force the defencemen to rush their play which then leads to a turnover (Either directly via a bad pass or indirectly by a pass that leads to a puck battle) and you don't need to throw big hits to do that. And I would also mention that his combination of size/speed/shot will lead to defenceman backing off more instead of pinching at the blueline, that's something that's obviously hard to measure the impact of but it's there.
At the end of the day even if not consistent he brings an element that not a lot of other players can. And in terms of team building it's better for your middle-6 players to have that unique element to their game then someone who brings what your top-6 already has but is just worse at it. For me if a team is going to pay a premium for Anderson then by all means trade him, but if the best you get is a late 1st/early 2nd round pick then there's little point in making that trade right now.
Some talk about him for his goal scorer capacity, I just saw that at as a bonus quite honestly because I don't judge him on the numbers of goals he scored or how he produce but how he play the game. We didn't pay him that kind of money to put the puck on the net like others sniper can around the league or like we do with Jonathan Drouin and Mike Hoffman for their offensive but for what he can bring with his unique package with the goals he can add!
For the dimension he can bring he is not overpay by much and if he have hit his full potential he would be underpaid! Individuallly, it's not really a bad contract but when you look at the big picture is where it's become something else at how he use his linemates, the ice time he need to make that kind of production, the fact he has change the way he play the game and over the time that kind of player has tendancy to slow down a lot.
On the forecheck, it's a lot better to attacking the d-man a la Lekhonen, more cerebral, than a la Anderson, more physical, but you need to have a good read of the game to do that because you need to have a good speed to attack the d-man at the right angle to cut the ice the most you can to restrain him and in the end even if you didn't touch the puck you can dictate the play on where he will go because he will only stay 1 option if you put him in the right pressure.
For Anderson, it will be harder for him if he try to play that part of the game more like Lekhonen because a lot of players are smarter than him and they will be able to beat him or avoid him the most of the time with a better understanding of the game or a faster execution. I think the best way for Anderson is to play at full speed with his big size like he do now. The key is not how many times or how hard you hit because you push you out of the play each times but to "sell" the idea you can at the d-man making him play faster to avoid to be hit forcing him to make a precipitate play who can create a turnover! To resume, the dman will never fear the read of the game of Andy but he will always be respectful and very honest toward what he can do on the physical side!
Like you said, his combination of size/speed/shot is the better tools he has from the offensive side and one thing I have forget to add in my text. This is vital for him because he create space for himself and the way he can gain speed and beat the d-man or be able to drive the net often because of that! He rarely need to play in restrain area until the offensive zone because of that!
For the trade, I understand you don't want to give him without a good return and I know Andy have a special package who has very hard to find, we wait a decade and maybe more for a guy with this kind of tools. I don't want to trade him at all cost, he doesn't hurt you now but at sometine it will if he keep playing the same way and becoming less physical. I can die with Josh Anderson the power forward on the 3 line with his salary but I don't want Josh Anderson the hockey player at any moment close to your team when we will be ready to compete!
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Something I have not said but my relation with Anderson it's like Love-Hate at some point. For the first and only time of my life, the Habs have trade for the guy I have wanted in the player of Josh Anderson. I felt in love with him in his breakout season in 2018-19, he would never get the credit he deserve for that season but one of the 3 best power forward in the NHL at that time and close to be the best through January 1st until the end of that season. A tank who gain a extra gear each month becoming unstoppable in every area of the game : offensive, defensive, fight, hit, PP, PK nothing he can't do and becoming a real threat every time he step on the ice! The player who his born to play with Caufield and Suzuki at the moment!
I've never be so excited by a trade involving the Habs but 10 minutes after I begin to have some doubt because of the return and the way Anderson played one year before it's just to good to be true because Columbus would never thought one second to let him go at first, and they would give him all the money they can if they thought the 2018-19 is the real one. Today, I understand why they choose to trade him instead ...
We have trade for the guys who has played like a monster in that year but this version of him just doesn't seem to exist anymore; same case for Drouin we trade for a player we never really see in Montréal! This is probably why I'm so hard on him like that because he has fooled me at the time I saw him only a couple of games and I never think I can be that wrong!