So,how can the Landsknecht has reworks is halberd and arquebus it soon be history 16th century to now is reworking
To be fair to you, I (since the original AoE3) had always thought it was odd having Dopplesoldniers and Landsknecht occupying the same two-handed sword-bearing role aesthetically.
As Landsknecht Mercs are Merc versions of Halberdiers (with Ronin being the Merc versions of actual Dopplesoldniers, ha), it makes more sense that they actually are armed with Halberds. Heck, call them Landsknecht Halberdiers to give even more sense (and readability) to the unit too.
As an aside, I have always thought a Landsknecht Merc Camp would have made a nice Minor Civ, as you could have Landsknecht Arquebusiers, Pikes, Swordsmen and Halberdiers, though the Germans Merc Camp upgrade is somewhat a nod to that.