i was wondering what would happen if X head cannon was equiped with Z metal tank and was the strongest monster on the field would pole position stop Z metal tank's effect?

Z metal tank actually becomes an equip spell card when being attached to x head cannon, as is normal for all union monsters, .. so yes, it would be effected by poleposition. and if your opponent has a monster that is higher than x head cannon's base attack, but lower than it's attack with z metal tank, then it would cause an infinite loop and thus be illegal.

trick:equip Sasuke Samurai with Mage Power nad Axe of Despair, then activate pole position. your opponent cannot place on the field any monster with ATK 500-3000.And face downs die immidetially

Actually, the face downs do not die immediately. They they put something down that when hit and put face up causes and infinite loop because of pole position, then pole position is immediately destroyed.

If pole position is destroyed in this manner, no monster is destroyed by pole positions effect

I think he may have went too fast for you... He meant that since the opponent can't play anything higher than Sasuke Samurai, he most likely is only going to play face-downs that he will destroy with Sasuke Samurai, "immediately", without flipping face-up.