When it comes to balance, the Giant Trial does 2 things:

1. It makes the game more difficult, because you'll have a (much) harder time to force some builds. You need to be more creative to meet your goals.
2. It allows for differently scaling biotica. The best example is Foxglove. Foxglove is absolutely bonkers without the 4 draft maximum and if you can force pick other harmonies. But in Giant Trial, it's a high risk/high gain strategy, because you need to squeeze harder for its exponential growth.

What you're talking about is more of category 1. No worries: it doesn't affect the game balance too much from a creation standpoint. When you get more experienced with Reus 2, you'll find that all of the eras can be 3 star-ed with Giant Trial. The better you are, the less luck you'll need with your draw. We've seen it done by a big number of players right now. :)

What I mean with Giant Trial being the base of balance, has much more to do with the second point. That is, some biotica will be easier to break with less limitations.

I hope that answers your question!

Regarding Sludge Corp. I believe the answer to that question is, only pick sludge corp if you get some good food biotica like elephants or blue whales.

However with this design I often find myself ending on calm eras just because the era 3s are so specific. Additional eras would help a lot with this new style. So would third eras either having global effects (e.g. solarpunk makes biospheres a tradeable invention) or letting you pick which city is the focus from all that qualify.