Yeah but the argument wasn't that similar packs can't work, Oceania and Australia are a perfect example; you just have to make sure that the visual language is different enough.
An Asia pack that heavily leans into the East Asian Architecture isn't something we've had so far and is something you can easily create a distinct visual language for. A safari pack that heavily leans into the safari aesthetic isn't something we've had so far (I'm talking safari hats etc.), etc. Yes those two examples have a base game theme; but with the new approach of animal pack + scenery that's a big bonus because then they just build on the existing stuff and don't have to make tons of scenery.
With Rainforest I just see less room to create something that is visually distinct, I'm not convinced on the different vibe really. Then I'd say it's just easier to go for a general Forest pack and lean more into the temperate aesthetic for your visual language. But hey, that's my personal opinion though, I understand that people disagree haha.
Eh, I'm going to be honest here and say that that last part is probably not how Frontier sees it.

I know that a bunch of people, including myself, were really looking forward to a Desert pack at one point and then Arid came along and it was exactly the opposite of what we wanted to see from a pack like that. Mountains can be exactly like that.
Regardless, there's a bigger world outside the forums here, I wouldn't rule out a Mountain pack at this point because here on the forums a few people had set their senses on those animals for the pack and they came in different packs.
Oh I can pinpoint that easily. We severely lack
temperate trees with long trunks and high canopies. The vast majority of temperate trees in the game have a 1/3 visible trunk and 2/3 canopy ratio; but very little temperate trees that are the opposite like for instance the scots pine or the rainbow eucalyptus are. Without those, you're stuck with big canopy trees that take a lot of space and don't allow you to make large forestscapes.