Not sure if it's been mentioned, as I've only skimmed the thread, so forgive me if I'm echoing here, but I do want to clarify that the fourth Monster that you get free for pre-ordering is not day one DLC. It's more comparable to the Mechromancer with Borderlands 2; if you preorder, you get a DLC character for free post-launch when it's complete. Everybody else pays for it, but everybody gets it at the same time.
Behemoth's little released footage shows missing animations and untextured, incomplete attacks that have probably not been balance tested yet, either, so it's definitely not complete content being cut from the game, and the rest of the planned DLC probably isn't even at that prototype stage yet.
Of course, the fact that this wasn't made properly clear in a majority of the marketing how this stuff works is just further proof of how godawful it's been. I've followed Evolve since Spring of last year and have been able to try both the Big Alpha and Beta, and have seen the inside information on the forums from the devs, so I've been able to see the game minus it's shady marketing attached, which is why I'll continue to support it. The marketing has been absolutely terrible about how they've handled things though. The free maps, free game modes, unsplit community and ability to test-drive DLC characters are all being swept under the rug to promote the paid DLC. And yes, you can try DLC characters before buying them. If you join a game in progress, the game will have a chance to drop you on a DLC character, and the devs are promoting doing this in custom games with friends who own the DLC so you can try before you buy. They're also posting telemetry data on the forums and even have patch notes with changes made after the Beta for a day one patch, and are extraordinarily active on the forums asking the community there for ideas and answering questions. And if you ask them about damage data? They'll end up posting charts and exact damage calculations. The devs are absurdly informative there.
Not that you'd ever know this without scrubbing the forums, because the marketing seems to be allergic to promoting any actual cool features in favor of pushing pre-orders.