Did you go to either if Blackburn or Preston by any chance? (Not a pop just interested) It's certainly not natural to his game but Preston in particular he was doing more than his fair share of work "defending from the front".
Ok another note. I think it's overstated this defending front the front especially with Walker, simply because the likes of Godden and Waghorn are willing to chase down lost causes or sacrifice positional awareness in the hope of forcing a mistake (which is great at certain times and is a valid tactic with plenty of joy against Fulham). Walker doesn't do that as often, but he he adds a different dynamic and looks a threat. How many times have we seen it in recent seasons where one of our strikers is isolated, or only one person in the box to attacks a cross etc. Walker is far better at saving his energy for what he is on the pitch for, scoring goals, yes it's a team sport and certain games will dictate that we need wags or Godden but Walker is more than deserving of a starting place at this level for me.
Just to add onto this, the fact that our attacking players have to do so much defensive work I think counts against them at times ( I completely support pressure from the front it's the right way to play, and suits us to the ground). Particularly O'Hare who I think would potentially have a far better attacking output if he wasn't having to bust a gut constantly, which although is a massive positive to his game, is only naturally going to slow his decision making through fatigue. It seems at times that if he was just a split second faster in the head he would score/assist far more often. That's based on nothing but an opinion but interesting to see what people think.