I think you've really surpassed yourself there DM on both counts. Hernandez may not contribute much other than finishing but Hernandez has already scored either the winning or equalising goal in four league games this season, winning us 10 points. van Persie is on great form this year but he is also not a particularly cool finisher and tends to go for power over precision.
Then to say United would prefer van Persie over Hernandez? I think Barcelona are the only team in the world that would say no to van Persie at the moment, that doesn't make Hernandez a bad player.
There is also no way Hernandez is on 100k a week. Even if he's on 75k a week this season that neglects the fact that he cost £12-18m less than Darren Bent.

Clueless as usual.
Actually yet again its you thats clueless, what on earth has Bent's fee got to do with anything?
Fabregas cost us 200k or so, Barca bought him for a fee that gets Arsenal around 40mil total. The same player, fee's mean NOTHING, they aren't an indication of anything, and your refusal to discuss the point and rely on arbitrary nonsense to suggest I'm clueless is really the general argument from anyone on here who has no point.
Again, if you missed the point, lets say he's on 75k, that is 75k you CAN'T pay another player, who could offer a LOT MORE to the team than Hernandez.
Option A spend 75k on a guy who can only poach, who is useless against the top teams, who will look clueless if asked to do anything but tap the ball in.
option B, spend 75k on a player who can tap the ball in the net, can pass well, can be involved in the build up play, can score freekicks, take corners, cross, can do tricks, can do one of those flip type celebrations and as really good at the trumpet.
When you're talking about the biggest team in the league, and spending 75k on wages, you don't have to have a player who is incredibly limited.
Its really that simple, RVP has nothing to do with this, Barca has nothing to do with this, Bent has nothing to do with this. There are better players than Hernandez who can bring a LOT more to the team. its really that simple. Transfer fee's are unimportant, when will CLUELESS people work that out, a club can sustain safely £X amount of wages, and if a player is on 75k a week, that is 75k less a week you could spend on another player.
I don't rate Hernandez as a good footballer, in recent games his woeful passing was embarrassing, watching him try to play football when he wasn't trying to tap in was laughable for the most part. He'd pass behind players making a run down the wing, more than once I believe he, with a relatively simple pass, just put it straight out, he's been very slow and holding the ball before deciding who to pass to and often gave it away.
Poaching is the easiest part of football, the best poachers are seemingly better at poaching, because they try to do nothing else, that will help you in some games and hurt you in many other games.
Rooney showed it the other year, when he simply decided to spend all his time sitting on the back four and being a poacher, he got goals, when he decides to play football and go deeper, he can, hernandez can't. Rooney had NEVER been "prolific" once in his career, and he never JUST went after goals. The one year that is all he tried to do, he scored a load of goals. Almost any player can, in a good team, deciding to do nothing but run in behind, get lots of goals. When the rest of the team is good enough, that works great, when the rest of the team isn't good enough, that works less well, when its not going well Rooney can drop deep, help the team and maybe set up a goal, Hernandez can't.
Most players can do what Hernandez does if they negate every other part of their game, most players can't do what a Xavi, or Messi, or Ronaldo, or even a Rooney.
You can spend 75k on a better player, start a better player, and lose nothing........... seems pretty simple to me.