What Poppy's ult doesn't do:
Doesn't suddenly make her able to have multiple dashes, doesn't suddenly make her cc any more reliable, doesn't stop any character from using their abilities / stopping others from helping Poppy's target. Poppy doesn't have an uncanny/overwhelming ability to force a 1v1 or lock someone down (ahem Zed, Vi, etc) she just requires the respect and smart planning for disengage and not having your most important characters getting wall stunned. Characters like Janna were annoying enough for Poppy; now we have Lulu, Thresh and Braum doing it better and being played in every game, and tons of middles that aren't phased by her, along with many tops and jungles who out do her in the areas you bring up as her "advantage" simply by being able to force and handle many more scenarios.
Emphasis on force/handle more scenarios. If she somehow could push lanes (lol tiamat) or actually was a solid sustained damage dealer she'd not be bad. Actually, the recent re-nerfing of Banshee's Veil is probably the biggest buff she's gotten in a while.