#1 Limited wrestling ability

The Phenom may have signature moves like the last ride, going old school, hell’s gate and the tombstone piledriver, but outside of those moves, his wrestling prowess is limited. That’s why whenever he’s in a match, Michael Cole emphasizes his ‘striking’ ability because, without that, he’s just a laboured mover in the ring.
You can’t compare the Undertaker’s ability to the athleticism of a John Cena or a Roman Reigns or The Rock. Without the strong booking he’s received, The Undertaker would just be another Karl Anderson, a big man with no aura or selling point.
And with age, Taker’s deficiencies in the ring have become more & more apparent. His last match at Wrestlemania 33, was the definition of why you should retire before you get found out.