I see Sunfire Cape as a tank item, and DMP as a juggernaut/bruiser item.
I can't think of many tanks, or at least any I play (Malph Cho Braum Thresh, and Blitz Gnar to a lesser extent), that really benefit from DMP's passives. Most of them already have ways to get in and disrupt the back line, so they don't really need Dreadnought (though it wouldn't hurt them), and most of them also drop off in damage pretty hard once they've unleashed their combo, which makes Crushing Blow both redundant and useless. This type of champ makes more sense to build Sunfire Cape on.
Juggernauts are tanky damage dealers, NOT tanks. Their purpose isn't to disrupt one team and peel for the other so much as to shred one or two squishies while ignoring the rest of the enemy team. Sunfire Cape doesn't make sense on them, because it's offensive against the team when they only want to murder one or two members. Further, they usually lack great engagement skills, and if they do have them (like Jax or Darius), it's hard to stick to the person they want to kill—and this is more important for juggernauts than tanks because their point is to stick to someone, not lock them down. DMP makes much more sense on these champions.
In a League that focuses more on bruisers than tanks, DMP will overshadow SF Cape, but that's not a bad thing, and there are still many champs that would rather build Cape than DMP.
However I am but a humble Bronzie so feel free to poke holes in that. Peace!