That is a problem though, invading the enemy jungle is a team effort (unless your lee sin).
Patently false. Champions that want to sit in their jungle farming 25 camps required to become relevant all make a nasty investment. Anybody who spends their gold on actual combat stats has free reign.
I'm actually quite pleased with feral flare. It makes farmer junglers relevant again, which by extension makes control junglers relevant again. I suspect soon Nunu's reign of terror shall begin again. It all reminds me of the season 1 jungler golden age.
This is a good summary of my own thoughts on the Flare. You can't just sit it in a void and say, "Gee, this sure is a good item," you have to think of the opportunity cost involved in building it.
Normally AD junglers would build Elder Lizard (or Golem if they were going full tank), and EL is really, really good for ganking junglers. When you build it, you're making a clear statement of intent; you're going to be ganking heavily, trying to have a presence, and trying to snowball your lane. Building towards Feral Flare is a statement similar to that, but in the opposite direction. The moment you have Madred's, you've shown (both to yourself and to the enemy team) that you intend to sit in jungle and farm for the first twenty or thirty minutes, at least.
FF is balanced for the same reason that nobody ever bought Wriggles in S3: If one jungler goes EL and the other goes FF, the match is essentially going to be 5v4 for much of the early and mid-game. If a FF jungler leaves jungle to gank, they're falling behind. If they get counterjungled, they're falling behind. If they do
anything but farm, they're falling behind. And if the enemy jungler tips the game against them before they leave the jungle with a bunch of fat items, it doesn't matter how many stacks they have unless they can carry alone.
But yes, I'm highly pleased with the Flare myself, both because farming junglers will be a thing again, and because it feels like a good risk-vs-reward sort of counter to the current high-impact early game junglers like Lee and Panth.