First of All, i never saw a Highlander except for the Kurgan showing superhuman strenght, and yes Duncan ripping of a metal railing but Second and more important, you're not talking about a marvel street hero without real physical super powers, you're talking of the guy that put down Dracula, that fought against Varnae, and that fough against demons and other things, Duncan has fought against immortals and mortals, but never fought demons or demigod like characters.Blade with the Sons of Midnight fought with Lilith, the max power that Duncan met in his life was Mythos.
AHighlanders heal faster than Blade?In tv series when Duncan gets hit by bullets goes down and take probably half and hour for him to heal, and remember that Blade doens't carry only a sword, he only needs to put out his uzi or 9mm gun and shoot him then seeing that he stands up starts a sword to sword fight, after seeing that stabbing Duncan doesn't works too, he perform a beheader hit, and the Highlander die.
We want to talk about Blade's resistance to injury?Get blood drained, get stabbed, cut, shot, and many other things, throw into walls and other obstacles, an Highlander would be unconscius after something like that.Or why don't we talk about Blade's strenght, he kick humans body like they are tennis balls, Duncan never show to be able to do something like that.
I give to Duncan that he has more experiecen than Blade will never possess until he lives for 400 years, but Blade has fought things that Duncan never met, so this put the fight on draw in terms of battle experience, but if we talk about physical skills, Blade has reaction times that can outmatch any highlander, the same for his agility and reflexes a human for Blade moves at slow motion.An Highlander hasn't got that kind of speed that Blade has.After a run for this money, i think that Blade would behead Duncan and ask himself how can a human be so damn skilled and heal so much faster, maybe it was a older daywalker that lose much of his strenght but was anyway a badass to deal with?
He'll never known it, now he just needs to rest cause Duncan perform a great fight.