Riot - it's wrong to compare Deadman's Plate to Sunfire and Randuins
Riot is upset that too many people are buying Deadman's Plate and not enough people are buying Sunfire, Randuins, Frozen Heart, etc. Their thinking is that all these items are tank/bruiser/juggernaut items and so tanks/brusiers/juggernauts should be buying each of them regularly depending on the situation.
But it's wrong to think of Deadman's plate as simply a durability item.
In fact, a better comparison group for Deadman's Plate might be: Boots of Swiftness, Righteous Glory, Black Cleaver, Triforce, etc. If you are an immobile champion, and adc's have a gazillion movespeed items, you need movespeed type utility to reliably catch and stick onto them. Likewise, if you are an immobile champion, you need movespeed type utility to reliably get back into position if you got out of position (to avoid getting caught, for example) or to escape the enemy team when you are split-pushing. The movespeed on Deadman's Plate is huge -- I cannot count the number of times it has allowed me to catch an enemy squishy, or run away from their team after I have been split pushing. The tankiness is valuable too -- I'd be too squishy if I picked a dedicated movespeed item in my bruiser or tank builds (e.g. I never built zephyr on Nasus or Malphite, of course). But that doesn't change the fact that the reason why I often buy Deadman's instead of or in addition to randuins/sunfire is because Deadman's provides movespeed which is so essential to bruisers and tanks.
If Riot wants Sunfire to compete with Deadman's Plate, they should give sunfire some sort of movespeed utility.
For example, give sunfire the additional passive "For each tick of damage inflicted by Sunfire Cape, Sunfire Cape gains 1 stack of Sunfire Cape stacks up to a maximum of w stacks. Each stack increases movespeed by x%. y Sunfire Cape stacks fall off per second when Sunfire Cape is not dealing damage".
This would give Sunfire Cape a mobility advantage that would allow it to compete with Deadman's Plate outside of the laning phase. In some ways it would be the inverse of Deadman's Plate -- Deadman's Plate gives you movespeed out of combat until you attack someone, while Sunfire Cape gives you movespeed in combat when you are damaging someone, giving you better stickiness as the fight progresses.
Maybe this solution in particular is not the right one. But you need to understand that the only way to make these other items competitive with Deadman's Plate (without simply nerfing Deadman's Plate's stats) is to give them some sort of conditional movement utility.
