That's why it's called creep--it starts off as "barely there". Plus this new agony condition is a horrible idea simply due to this: "LFM new dungeon, MUST have X agony resistant gear". Basically, access to the dungeon is limited to gear. Yes, dungeons aren't as difficult as they once seemed. But added a silly mechanic such is agony is hardly a solution to delivering harder content.
Except they said themselves, you only need the infusion if you're going to be hardcore grinding the dungeon, in which case you'll get the new gear. If you aren't grinding the new dungeon hardcore, you can just do it in rares/exotics like normal and you don't have to worry.