He gets pushed off the puck all the time, he does not use his size to get body position, and 99% of the time he will try to finesse a puck through people instead of leaning on them and making space for himself or others. Hughes is more likely to put a shoulder into someone to facilitate a breakout than Myers is. I wouldn't call him soft but hits and fights aren't the only ways to use size either.
I disagree with your assessment so we'll have to agree to disagree.
But taking your assessment at face value, not using his size to his full advantage is not the same as "complete lack of physical play." When Myers does lean on a player that player usually does go flying. We've seen some big hits from Myers where if Hughes threw the same type of hit the result would be drastically different. Hits and fights aren't the only ways to "use size", but you made the claim that Myers exhibits a "complete lack of physical play" so I ask what's your measure of physical play.
Myers isn't Chara strong but he is listed at 229lbs and is obviously a different sized player from Hughes. So I don't think you can really compare. Hughes has learned that he needs to more proactive in putting a shoulder into someone where as Myers can simply push guys off pucks. Myers putting a shoulder into someone might end up being a hit to the head. At the same time I would say that Myers' first step from a stationary position isn't all that powerful which might be what you are seeing. But that wouldn't equate to "complete lack of physical play."
Hughes looks like the hardest working Dman out there but that is mostly due to necessity of being a smaller guy.