In terms of gem dragon drop rate in the Soulforge, there is no documented evidence that RNG is skewed. Quite the opposite, in fact.
Am I saying this games doesn’t use predatory monetization tactics? No, it most certainly does, but not in every situation. There are lots of valid criticisms on these forums, and also a lot of criticisms not backed up by actual data. That’s part of why I enjoy helping to collect community data - we would never have known about the 1-2-3 combination of Dungeon doors being impossible to give a Perfect Run had the community not gathered data, for example! Luckily that issue was corrected, and we can use ongoing data for other things to verify whether things are skewed 