Also, note that the capped lifespan for Infernals was only added in the same book. It wasn't a core trait of Infernals.
That's why I utterly ignore it. It was only put in to force you towards the Devil Tiger path, or force you to Essence-escalate. And I consider neither of these to be desirable.
But the real reason that the Devil Tiger path is lame is that because by the time you can access it, you're an Essence 6 Infernal. You've taken a bunch of personality-changing charms. More than that, you've internalised the use of your own charms. Infernal Charms work by giving you a hammer and letting you turn your problems into nails. If you've invested in GSNF and expansions, you will have internalised the Malfean mindset that problems can be solved through blatant force because blatant force is how you solve your problems and
it clearly works for you. Same as heavy investment in Kimberyian poisons. You
will use poisons a lot and rely on weakening opponents with horrific painful debuffs, because that's an incredibly effective playstyle. If you've invested in Metagaos heavily, you're going to be getting stronger by eating things and always hungry. That's part of who you are.
By the time you're able to become a Devil Tiger, you've already internalised the mindset of the mix of Yozi Charms you've learned - especially if you do the common way of learning Yozi Charms, which is getting your Charms based off your personality and your desires. You've created a watercolour using the Yozi Charms as paints, which describes their character as you currently are. The Devil Tiger Charmset is
pointless, because any player who can write the extensive homebrew required for a working balanced Devil Tiger is a good enough Charm writer to just get the same effects in the Yozis they already have. There's no need for a personalised Charmset, because by the time you could learn it, you've already made your Yozi Charmset into your own. And if you can't contort the existing Yozi Charmsets into doing what your character wants to do, you can't write a proper Devil Tiger tree - because Devil Tiger trees should also be Yoziesque trees that follow symbolic logic and don't take you exactly where you want to go.
Keris would laugh at the idea of the Devil Tiger tree. What
point would there be in her doing it? What kind of effect that she would want can she not find or invent in Metagaos, Adorjan or Kimbery (with occasional forrays into other Yozis for easy-to-access useful things, like LSD)?