Usually a player has no right to call metagaming on the GM. You are assuming a lot about your foes. Maybe your enemy is under the employ of a BBEG whos spies have informed him about your abilities and he has warned his minions. Maybe the caster simply has fought somebody with Step-Up before and decided to invest in appropriate countermeasures. Step-up may or may not be a bit unusual, bur reach weapons certainly are not, and the good old acrobatics trick would foil a reach weapon user just as easily.
A caster could get a good acrobatics if they want one, between dex and traits to add Acrobatics as a class skill or multiclassing. Nevertheless, they are investing part of their character in this defense, as opposed to just out and out killing you, so you should be happy.
Honestly it would be easier for a caster to simply pick up Combat Casting, or Mirror Image, or Greater Invisibility, or Displacement, or Fly, or any of the other plentiful options at his disposal for foiling a pure melee character. Your GM is throwing you a bone by having them *not* do that. I recommend you not spit it back in his face.
I think you're giving the DM too much credit. Good DMs metagame and you don't mind it at all. Really good DMs metagame and you love it. A bad DM metagames and you feel cheated. In fact, I'm not even sure how you can think a DM who is using blackflipping wizards to make a player feel useless even has an idea what he's doing.
Hell, I remember pulling that crap when I was first starting out. When you don't have a masterful grasp of the system, you generally become very reactionary to increasing character ability. I mean, you should always be reacting to the players, but when you're new and bad, you can't zoom out far enough to find interesting solutions to the problem of a sticky fighter. I cringe to remember things I did to my friends in high school to keep a rogue from getting his sneak attacks.