I assure you that no one, regardless of player level or arena status, is winning 4,000 T-Rex DNA from their incubators. It just doesn’t happen. Yeah, players in Sorna Marshes get a ton of Gen 2 DNA that isn’t particularly useful, but we’re not the only ones, I assure you.
It takes a lot of time and grinding to get Legendary and Unique creatures. I’ve been playing since the global release in June and only recently unlocked Indominus Rex–a lot of players have had it for waaay longer than I have. Some players spend actual money on incubators, but generally speaking, it’s all about putting in that time—regardless of whether you spend money or are strictly free-to-play.
Put in the time to hunt dinos in your free time (making note of where and when Epics tend to spawn), put in the hours visiting showcase event drops, and you’ll slowly start to see improvements.
Best of luck!