Ok, so I watched the play at .25 speed on youtube. In doing so, it's clear, Marcus DID NOT take a bad angle or put his head down and whiff. What did happen was DK pumped the brakes and did a little fake juke to the inside which caused Marcus to freeze because if DK had cut inside of him he would of been gone also.
This is simply a very hard tackle to make coming from across the field and to multiply the complexity of it, you have a WR built like Derrick Henry with 4.3 speed.
Had DK kept running in a straight line, without the fake, Marcus is in position to make the tackle...and I believe he would have in that case.